Last week I delivered the webinar on how to design and deploy workflows using SharePoint Designer 2013 for Project Server 2013. You can download the deck from
You need to configure Workflow Manager 1.0 before you create Project Server workflow using SharePoint Designer 2013. Below link contains information on how to install and configure Workflow Manager
You can find workflow logic for the sample workflow I created during demo on slide number 12. Below is snapshot of the sample workflow from SharePoint Designer.