You can't really have roof 'prefabs'. Roofs are often made to fit particular structures and having set roofs would lead to much lots of the same. The best option would be to create a guide on how basic roofs can be created but even then it's pretty easy.
What comes easy for some may be very hard for others. I wrote a guide for building slanted roofs, and it goes step by step with no fluff. You can follow it here if you want to learn how to build roofs yourself.