Hi,
I'm afraid at the moment you can not install any application through the Application Vault to the root of your domain. You can of course install Drupal or any other application by hand to the root of your domain, just not when using the Application Vault.
We would typically recommend you use the Application Vault to upload any themes or plugins you need, if that is possible for your application:
Application Vault >> Blog Software >> Drupal >> install name
For where the files themselves are located please see here:
https://support.blacknight.ie/262/lo...ion-vault.html