If the project is not registered in RERA and does not have any registration certificate, then builder cannot advertise, book, sell, invite purchaser or investors for selling purposes.
So, if you are planning to work on a new project than we would suggest you get registration certificate first because without it you will not be able to sell,advertise or market it. If you have completed your project or near completion than you should acquire completion certificate. Otherwise, you will have to apply for regular registration in RERA. Moreover, the projects with NOC from local authorities will also have to registered themselves.