I'm going to be honest with you. I'm an inspector and posts like this freak me out. Please don't build this. If you don't know how the basics of framing, code requirements, how to size members based on local design criteria, then this could end poorly. If your posts are 4x4s, I'd bet your deck is from the early 2000s or earlier. It's probably already undersized compared to current codes. Adding a roof on top without taking into account all factors is a bad idea.