One potential issue for many organisations with Project Server 2013 is that users need access to Central Admin if they want to build the OLAP Cube. Usually the PMO / PWA Admins would not have access to Central Admin, they only have access to Project Web App. If they want to build the OLAP Cube on demand, they would need to raise a request to the team that manages SharePoint Central Admin. To get around this, they can use PowerShell from the local workstation. The script can be downloaded from the script gallery below:
Once the script is downloaded, the uri will need to be updated to use the correct URL, update the http://vm753/pwa part of the URL. You will also need to update the cube GUID. You can get the cube GUID from the URL in Central Admin when you access the OLAP cube settings page. See the highlighted URL below:
Obviously someone with access to Central Admin will need to get the OLAP Cube GUID for you.
The users running the script will need to correct permissions in Project Server. They will need Manage Cube Build service and Mange Site Services.