If I am understanding this correctly, your coop is 10x10, with an 8 foot front wall and 6 foot back wall. You’re making it in panels to disassemble and then reassemble.
Sounds like a fun project.
I Would:
Using 12 foot 2x4s make a few simple rafters - this will give a 1 foot overhang on the...
Are you making a lean-to style roof?
If you are, why do you need an angle? The front is 8 feet and the back is 6, correct? Rafters from front to back, theres your angle. Over-hang a few inches or feet on both sides for water shed and your good to roll.
Or are you asking for an angle to cut...