I was reviewing your sketch and realized that some words appear cut off. Could you get me another pic, pretty please?@Fishychix
I hope these make sense....
View attachment 2461058
The board going across the ends of the rafters is called a fascia board. On a human house it holds the gutters. On my coop (no gutters) it acts as part of my baffle to slow wind and keep rain out..
View attachment 2461060
Same coop. See how it is open underneath? That's for airflow.
View attachment 2461062
Inside that exact same corner. This pic has a LOT of data...
Darker board going upward is a wall stud. Rafter sits directly above wall stud to transfer load. In a human house 16" on center is pretty standard. In a shed or coop wider spacing is ok. Mine are 2' on center. You can also see the no no critter hardware cloth and another part of my baffle attempt. I have short 2x4's in between the rafters to hold the wire and spaced back from the wall to let air move.
View attachment 2461088
You would need to build something like this to extend your wall. Your studs would be 21" with a 2x4 above and below them to equal 24".
I would DEFINITELY draw your plan on graph paper so if you need to change an angle to make the most of each board you can just by erasing.
Oh and both the high side of my roof and the low side have open soffits.
Thank you!

I should have been spending the super cold days dry fitting stuff in the garage, but it’s super cold in there too. And my freezing fingers don't wanna do much, lol 
