diff --git a/crates/proton-drive-sdk/src/client.rs b/crates/proton-drive-sdk/src/client.rs
index 6320fc6..9e6475e 100644
--- a/crates/proton-drive-sdk/src/client.rs
+++ b/crates/proton-drive-sdk/src/client.rs
@@ -15,8 +15,8 @@ use proton_sdk::crypto::PrivateKey;
 use proton_sdk::error::{ProtonError, Result};
 use proton_sdk::http::ApiHttpClient;
 use proton_sdk::crypto::{
-    generate_node_hash_key, generate_node_key, verify_detached, ContentKey, VerificationKeyRing,
-    VerificationStatus,
+    build_volume_creation_material, generate_node_hash_key, generate_node_key, verify_detached,
+    ContentKey, VerificationKeyRing, VerificationStatus,
 };
 use proton_sdk::ids::{AddressId, DriveEventId, LinkId, NodeUid, ShareId, VolumeId};
 use proton_sdk::session::ProtonApiSession;
@@ -40,7 +40,7 @@ use crate::dtos::{
     RevisionCreationResponse, RevisionDto, RevisionResponse, RevisionUpdateRequest,
     LatestVolumeEventResponse, PhotosAttributesDto, ThumbnailBlockListRequest,
     ThumbnailBlockListResponse, ThumbnailCreationRequest, ThumbnailDto, TimelinePhotoListResponse,
-    VolumeEventDto, VolumeEventListResponse, VolumeTrashResponse,
+    VolumeCreationRequest, VolumeEventDto, VolumeEventListResponse, VolumeTrashResponse,
 };
 use crate::photos::{PhotoUploadMetadata, PhotosTimelineItem};
 use crate::cache::DriveEntityCache;
@@ -165,7 +165,7 @@ impl ProtonDriveClient {
         entity_repository: Arc<dyn CacheRepository>,
     ) -> Self {
         Self {
-            http: session.http().clone(),
+            http: session.http().with_base_route("drive/"),
             account: AccountClient::new(session, mailbox_password),
             cache: Arc::new(Mutex::new(DriveCache::default())),
             entities: DriveEntityCache::new(entity_repository),
@@ -1541,7 +1541,17 @@ impl ProtonDriveClient {
             return Ok(());
         }
 
-        let response: MyFilesShareResponse = self.http.get("v2/shares/my-files").await?;
+        // Mirrors C# `NodeOperations.GetOrCreateMyFilesFolderAsync`: a brand-new
+        // account has no My Files volume yet, so the share lookup fails. Create
+        // the volume, then re-read it through the normal path to populate caches.
+        let response: MyFilesShareResponse = match self.http.get("v2/shares/my-files").await {
+            Ok(response) => response,
+            Err(e) if is_my_files_missing(&e) => {
+                self.create_volume().await?;
+                self.http.get("v2/shares/my-files").await?
+            }
+            Err(e) => return Err(e),
+        };
         let volume_id = response.volume.id.clone();
         let share_id = response.share.id.clone();
 
@@ -1566,6 +1576,42 @@ impl ProtonDriveClient {
         Ok(())
     }
 
+    /// Create the account's main volume (root share + root folder).
+    ///
+    /// Mirrors C# `VolumeOperations.CreateVolumeAsync`: build the root share and
+    /// folder crypto material against the default address's primary key and
+    /// `POST volumes`. The server-side state is then read back by the caller
+    /// ([`ensure_my_files`](Self::ensure_my_files)) via the normal share lookup,
+    /// so no local cache priming is needed here.
+    async fn create_volume(&self) -> Result<()> {
+        let mut timer = self.telemetry.start("create_volume");
+
+        let address = self.account.default_address().await?;
+        let address_keys = self.account.address_private_keys(&address.id).await?;
+        let address_key = address_keys
+            .get(address.primary_key_index)
+            .ok_or_else(|| ProtonError::invalid_operation("default address has no primary key"))?;
+
+        let material = build_volume_creation_material(address_key, "root")?;
+
+        let request = VolumeCreationRequest {
+            address_id: address.id.clone(),
+            address_key_id: address.primary_key_id.clone(),
+            share_key: material.share_key_armored,
+            share_passphrase: material.share_passphrase,
+            share_passphrase_signature: material.share_passphrase_signature,
+            folder_name: material.folder_name,
+            folder_key: material.folder_key_armored,
+            folder_passphrase: material.folder_passphrase,
+            folder_passphrase_signature: material.folder_passphrase_signature,
+            folder_hash_key: material.folder_hash_key,
+        };
+
+        let _: proton_sdk::api::ApiResponse = self.http.post("volumes", &request).await?;
+        timer.success();
+        Ok(())
+    }
+
     async fn root_share_key(&self) -> Result<PrivateKey> {
         self.ensure_my_files().await?;
         Ok(self
@@ -2209,6 +2255,18 @@ fn read_full_block<R: Read>(reader: &mut R, buf: &mut [u8]) -> Result<usize> {
 
 /// Group node uids by volume, preserving order, so each volume's links are
 /// batched into a single request family (C# groups by `VolumeId`).
+/// Whether a `v2/shares/my-files` error means the account has no My Files volume
+/// yet (and so one must be created). C# catches [`ResponseCode::DoesNotExist`];
+/// in practice a fresh account's lookup also surfaces as a bare HTTP 404, so
+/// both are treated as "missing".
+fn is_my_files_missing(error: &ProtonError) -> bool {
+    matches!(
+        error,
+        ProtonError::Api(e)
+            if e.code == proton_sdk::api::ResponseCode::DoesNotExist || e.http_status == 404
+    )
+}
+
 fn group_by_volume(uids: &[NodeUid]) -> Vec<(VolumeId, Vec<LinkId>)> {
     let mut groups: Vec<(VolumeId, Vec<LinkId>)> = Vec::new();
     for uid in uids {
diff --git a/crates/proton-drive-sdk/src/dtos.rs b/crates/proton-drive-sdk/src/dtos.rs
index f1ac4f6..35b2a14 100644
--- a/crates/proton-drive-sdk/src/dtos.rs
+++ b/crates/proton-drive-sdk/src/dtos.rs
@@ -6,7 +6,7 @@
 
 use serde::{Deserialize, Serialize};
 
-use proton_sdk::ids::{AddressId, DriveEventId, LinkId, ShareId, VolumeId};
+use proton_sdk::ids::{AddressId, AddressKeyId, DriveEventId, LinkId, ShareId, VolumeId};
 
 /// `GET v2/shares/my-files`
 #[derive(Debug, Deserialize)]
@@ -429,6 +429,33 @@ pub struct FolderCreationRequest {
     pub signature_email: String,
 }
 
+/// `POST volumes` request body — create a new volume with its root share and
+/// root folder. Mirrors C# `VolumeCreationRequest`. All PGP fields are armored
+/// strings produced by [`proton_sdk::crypto::build_volume_creation_material`].
+#[derive(Debug, Serialize)]
+pub struct VolumeCreationRequest {
+    #[serde(rename = "AddressID")]
+    pub address_id: AddressId,
+    #[serde(rename = "AddressKeyID")]
+    pub address_key_id: AddressKeyId,
+    #[serde(rename = "ShareKey")]
+    pub share_key: String,
+    #[serde(rename = "SharePassphrase")]
+    pub share_passphrase: String,
+    #[serde(rename = "SharePassphraseSignature")]
+    pub share_passphrase_signature: String,
+    #[serde(rename = "FolderName")]
+    pub folder_name: String,
+    #[serde(rename = "FolderKey")]
+    pub folder_key: String,
+    #[serde(rename = "FolderPassphrase")]
+    pub folder_passphrase: String,
+    #[serde(rename = "FolderPassphraseSignature")]
+    pub folder_passphrase_signature: String,
+    #[serde(rename = "FolderHashKey")]
+    pub folder_hash_key: String,
+}
+
 /// `POST v2/volumes/{vid}/folders` response.
 #[derive(Debug, Deserialize)]
 pub struct FolderCreationResponse {
diff --git a/crates/proton-sdk/src/account.rs b/crates/proton-sdk/src/account.rs
index 8d701de..b7ca3d8 100644
--- a/crates/proton-sdk/src/account.rs
+++ b/crates/proton-sdk/src/account.rs
@@ -20,7 +20,7 @@ use tokio::sync::Mutex;
 use crate::crypto::{self, PrivateKey, PublicKey};
 use crate::error::{ProtonError, Result};
 use crate::http::ApiHttpClient;
-use crate::ids::AddressId;
+use crate::ids::{AddressId, AddressKeyId};
 use crate::session::ProtonApiSession;
 
 use dtos::{
@@ -37,6 +37,8 @@ pub struct Address {
     pub status: i32,
     /// Index, within the decrypted key list, of the primary key.
     pub primary_key_index: usize,
+    /// Id of the address's primary key (the `AddressKeyID` for write requests).
+    pub primary_key_id: AddressKeyId,
 }
 
 /// Resolves account keys needed to decrypt Drive metadata.
@@ -263,6 +265,7 @@ impl AccountClient {
 
         let mut keys = Vec::new();
         let mut primary_key_index = None;
+        let mut primary_key_id = None;
 
         for key_dto in &dto.keys {
             if !key_dto.is_active() {
@@ -295,6 +298,7 @@ impl AccountClient {
                 Ok(key) => {
                     if key_dto.is_primary() && primary_key_index.is_none() {
                         primary_key_index = Some(keys.len());
+                        primary_key_id = Some(key_dto.id.clone());
                     }
                     keys.push(key);
                 }
@@ -306,6 +310,8 @@ impl AccountClient {
 
         let primary_key_index = primary_key_index
             .ok_or_else(|| ProtonError::invalid_operation(format!("address {} has no primary key", dto.id)))?;
+        let primary_key_id = primary_key_id
+            .ok_or_else(|| ProtonError::invalid_operation(format!("address {} has no primary key", dto.id)))?;
 
         let address = Address {
             id: dto.id.clone(),
@@ -313,6 +319,7 @@ impl AccountClient {
             order: dto.order,
             status: dto.status,
             primary_key_index,
+            primary_key_id,
         };
 
         Ok((address, keys))
diff --git a/crates/proton-sdk/src/crypto.rs b/crates/proton-sdk/src/crypto.rs
index 0154f3d..bbec312 100644
--- a/crates/proton-sdk/src/crypto.rs
+++ b/crates/proton-sdk/src/crypto.rs
@@ -16,7 +16,10 @@ mod verify;
 
 pub use content::ContentKey;
 pub use derive::derive_key_passphrase;
-pub use encrypt::{generate_node_hash_key, generate_node_key, GeneratedNodeKey};
+pub use encrypt::{
+    build_volume_creation_material, generate_node_hash_key, generate_node_key, GeneratedNodeKey,
+    VolumeCreationMaterial,
+};
 pub use errors::CryptoError;
 pub use keys::{decrypt_armored_with_keys, PrivateKey};
 pub use srp::{generate_proofs, SrpProofs, DEFAULT_BIT_LENGTH};
diff --git a/crates/proton-sdk/src/crypto/encrypt.rs b/crates/proton-sdk/src/crypto/encrypt.rs
index 692359a..c15b165 100644
--- a/crates/proton-sdk/src/crypto/encrypt.rs
+++ b/crates/proton-sdk/src/crypto/encrypt.rs
@@ -146,6 +146,76 @@ pub fn generate_node_hash_key(node_key: &PrivateKey) -> Result<String, CryptoErr
     encrypt_and_sign(node_key.key(), Some(node_key), &bytes, false, false)
 }
 
+/// The encrypted/locked material for a new volume's root share + root folder.
+///
+/// Mirrors the output of C# `VolumeOperations.GetCreationRequest`: a fresh root
+/// share key and root folder key (each Ed25519 + X25519, locked with a random
+/// passphrase), plus the passphrases/name/hash-key encrypted into the request
+/// shape the `volumes` endpoint expects.
+pub struct VolumeCreationMaterial {
+    /// Locked root share key (armored secret key) — `ShareKey`.
+    pub share_key_armored: String,
+    /// Share passphrase encrypted (encrypt-only) to the address key — `SharePassphrase`.
+    pub share_passphrase: String,
+    /// Detached signature over the share passphrase by the address key.
+    pub share_passphrase_signature: String,
+    /// Root folder name encrypted + inline-signed to the share key — `FolderName`.
+    pub folder_name: String,
+    /// Locked root folder key (armored secret key) — `FolderKey`.
+    pub folder_key_armored: String,
+    /// Folder passphrase encrypted (encrypt-only) to the share key — `FolderPassphrase`.
+    pub folder_passphrase: String,
+    /// Detached signature over the folder passphrase by the address key.
+    pub folder_passphrase_signature: String,
+    /// Folder hash key encrypted + inline-signed to the folder key — `FolderHashKey`.
+    pub folder_hash_key: String,
+}
+
+/// Build the crypto material for creating a volume's root share and folder.
+///
+/// Mirrors C# `VolumeOperations.GetCreationRequest`:
+/// - root share key + folder key are generated and locked with random passphrases;
+/// - the **share** passphrase is encrypted (encrypt-only) to `address_key` with a
+///   detached signature by the address key (it is the address key that unwraps it);
+/// - the **folder** passphrase is encrypted (encrypt-only) to the share key with a
+///   detached signature by the address key;
+/// - the folder **name** (`"root"`) is encrypted + inline-signed to the share key;
+/// - the folder **hash key** (32 random bytes) is encrypted + inline-signed to the
+///   folder key. All inline/detached signatures are made by `address_key`.
+pub fn build_volume_creation_material(
+    address_key: &PrivateKey,
+    root_folder_name: &str,
+) -> Result<VolumeCreationMaterial, CryptoError> {
+    let share = generate_node_key()?;
+    let folder = generate_node_key()?;
+
+    let share_passphrase = address_key.encrypt(&share.passphrase)?;
+    let share_passphrase_signature = address_key.sign_detached(&share.passphrase)?;
+
+    let folder_name = share
+        .key
+        .encrypt_and_sign(address_key, root_folder_name.as_bytes(), true, false)?;
+    let folder_passphrase = share.key.encrypt(&folder.passphrase)?;
+    let folder_passphrase_signature = address_key.sign_detached(&folder.passphrase)?;
+
+    let mut hash_key = [0u8; 32];
+    rand::thread_rng().fill_bytes(&mut hash_key);
+    let folder_hash_key = folder
+        .key
+        .encrypt_and_sign(address_key, &hash_key, false, false)?;
+
+    Ok(VolumeCreationMaterial {
+        share_key_armored: share.locked_armored,
+        share_passphrase,
+        share_passphrase_signature,
+        folder_name,
+        folder_key_armored: folder.locked_armored,
+        folder_passphrase,
+        folder_passphrase_signature,
+        folder_hash_key,
+    })
+}
+
 /// Encrypt `data` to `recipient`, optionally inline-signing with `signer`, and
 /// return the armored PGP message. Mirrors C# `PgpEncrypter.EncryptAndSign`
 /// (and the encrypt-only path when `signer` is `None`).
@@ -260,6 +330,51 @@ mod tests {
             .expect("verify detached signature");
     }
 
+    #[test]
+    fn volume_creation_material_round_trips() {
+        // Stand-in for the account's primary address key.
+        let address_key = generate_node_key().expect("generate address key");
+
+        let material =
+            build_volume_creation_material(&address_key.key, "root").expect("build material");
+
+        // The share passphrase is encrypted to the address key and unlocks the
+        // root share key; its detached signature verifies against the address key.
+        let share_pp = address_key
+            .key
+            .decrypt_armored_message(&material.share_passphrase)
+            .expect("decrypt share passphrase");
+        address_key
+            .key
+            .verify_detached_signature(&material.share_passphrase_signature, &share_pp)
+            .expect("verify share passphrase signature");
+        let share_key = PrivateKey::from_armored(&material.share_key_armored, &share_pp)
+            .expect("unlock share key");
+
+        // The folder passphrase is encrypted to the share key and unlocks the
+        // root folder key; its detached signature verifies against the address key.
+        let folder_pp = share_key
+            .decrypt_armored_message(&material.folder_passphrase)
+            .expect("decrypt folder passphrase");
+        address_key
+            .key
+            .verify_detached_signature(&material.folder_passphrase_signature, &folder_pp)
+            .expect("verify folder passphrase signature");
+        let folder_key = PrivateKey::from_armored(&material.folder_key_armored, &folder_pp)
+            .expect("unlock folder key");
+
+        // The folder name is encrypted to the share key; the hash key to the folder key.
+        let name = share_key
+            .decrypt_armored_message(&material.folder_name)
+            .expect("decrypt folder name");
+        assert_eq!(name, b"root");
+
+        let hash_key = folder_key
+            .decrypt_armored_message(&material.folder_hash_key)
+            .expect("decrypt folder hash key");
+        assert_eq!(hash_key.len(), 32);
+    }
+
     #[test]
     fn node_hash_key_round_trips_under_node_key() {
         // The folder hash key is 32 random bytes encrypted to the folder's own
diff --git a/crates/proton-sdk/src/http.rs b/crates/proton-sdk/src/http.rs
index 1caee7c..476a683 100644
--- a/crates/proton-sdk/src/http.rs
+++ b/crates/proton-sdk/src/http.rs
@@ -39,6 +39,12 @@ pub struct Tokens {
 #[derive(Clone)]
 pub struct ApiHttpClient {
     inner: Arc<Inner>,
+    /// Extra path segment prepended to every request path (after `base_url`,
+    /// before the per-call `path`). Mirrors C# `session.GetHttpClient(baseRoute)`
+    /// — the Drive client targets `…/drive/` while account/auth calls stay at the
+    /// root. Empty by default. Lives on the outer struct (not `Inner`) so clones
+    /// can carry different prefixes while sharing one token/telemetry store.
+    route_prefix: Arc<str>,
 }
 
 struct Inner {
@@ -77,9 +83,22 @@ impl ApiHttpClient {
                 tokens: Mutex::new(tokens),
                 telemetry: std::sync::Mutex::new(NoopTelemetry::shared()),
             }),
+            route_prefix: Arc::from(""),
         })
     }
 
+    /// Derive a clone that prepends `route` to every request path, sharing this
+    /// client's token store, telemetry sink and connection pool. Mirrors C#
+    /// `session.GetHttpClient(baseRoute)`: the Drive client passes `"drive/"` so
+    /// its routes resolve under `…/drive/` while auth/account calls (and token
+    /// refresh) stay at the root. `route` should end in `/`.
+    pub fn with_base_route(&self, route: impl Into<Arc<str>>) -> Self {
+        Self {
+            inner: Arc::clone(&self.inner),
+            route_prefix: route.into(),
+        }
+    }
+
     /// Snapshot the current tokens (e.g. to persist for a later `resume`).
     pub async fn current_tokens(&self) -> Tokens {
         self.inner.tokens.lock().await.clone()
@@ -274,7 +293,12 @@ impl ApiHttpClient {
         body: Option<&B>,
         access_token: &str,
     ) -> Result<reqwest::Response> {
-        let url = format!("{}{}", self.inner.base_url, path.trim_start_matches('/'));
+        let url = format!(
+            "{}{}{}",
+            self.inner.base_url,
+            self.route_prefix,
+            path.trim_start_matches('/')
+        );
         send_retrying(&self.inner.config.retry_policy, || {
             let mut request = self
                 .inner