This may be basic to most, but I'm recently retired from an office job and I'm trying my hand at carpentry. How do I determine the proper angle cut for my rafters? My room is 16'x16' OD with a simple pitch roof line. The ridge beam is 2x8x18. The wall sill is a 2x8 on top ofr a double brick wall. I've already ruined several rafters trying to get it right. Any help will be appreciated.

Don