Best Way to Tie in New Porch Walls

[Needing Advice]

I'm going to be roofing over and screening in my upstairs deck. It is attached to the house via a ledger board at the floor joist. When I build the walls, what is the best way to tie them into the existing house? Unfortunately there aren't any existing studs where the new porch walls will butt up to the house.

Should I tear out some drywall inside and put in a 2x4 corner at each of the connection points? The wall is a gable end wall so I don't see how I could overlap the house top plates and new porch top plates without sistering on some boards to get around the 2x6 gable end ceiling joist that will be in the way.

As extra support would it be a dumb idea to tie the new walls in by attaching the porch top plates to the existing ceiling joist in a manner similiar to lookouts? Or would the 2x4 corner posts be enough support?

Hope this isn't too confusing just trying to get some fresh ideas.

Thank you.

[PeterD]

Last one I did, I tore off the sheathing on the outside, dropped in a couple of studs for each wall I was adding, and put the sheathing back on. Much easier and cleaner than going after the drywall!