When I did framing I worked with some guys that would sheet the whole roof. They would build the 1st deck, then 2nd, followed by the roof; all on top of one another. They would build it in the parking lot. Crane set up the 1st deck. everyone would throw up the prefab walls. then followed by 2nd deck. so on....
They did this mostly on town homes or apps. I didn't like it personaly.
You ran your but off on crane day getting everything up. If you ran into problems it was a mess. plus a lot of patch work.
We have also put all the cornish on the walls before standing them.
Just build a ladder to match overhang. Get the distance down, layout ladder blocks to match truss (so they can be nailed to truss tails).Just be careful when setting the truss, if they sit down on the blocks it can tear off the cornish.
This worked good. Only thing to do off ladders is the returns.
We've Done porches like this as well. put them on the wall, before standing them. It makes the wall heavy as....