I subbed out the framing when I did this exact project about 15 years ago. As I recall the framer cut the ends of the floor joists to add a rim joist and then 3/4" ply over top. The floor joists I think only had a minimal notch out of the corner so no additional blocking or sistering was required.
he then built a false mini roof tacked to the outside that matched up on the sides like this