If you dont have an autonumbering system for your projects on project server, or are looking for a better one that does not violate your suport aggrement like one that uses direct db access.**
**https://support.microsoft.com/kb/841057 (See seventh bullet, in bulleted list)
Check out Fluent Pro!
Here are some great resources on the solution:
http://www.projectserver2010blog.com/2014/02/generation-of-custom-project-ids.html?m=1 – How to use Fluent Pro
http://www.fluentpro.com/productsformulas2013.html – Fluent pro download page
Some troubleshooting hints:
Make sure you have DisableLoopBackCheck and BackConnectionHostNames in place on your servers
Make sure you use an account that has deploy solution capabilities to install.
make sure that solution retracts fully from your PWA site if you should need to retract, remove, and re-install. Make sure that you deactivate from your site collection, then remove from farm solutions.
Install should work using the executable from FluentPro.