Here's one thread that might help you, also do a search for woods coop and other threads will come up.
https://www.backyardchickens.com/threads/woods-coop-confusion.1218521/
What style shed are you planning on getting built? I'm guessing by your temps and snow, you must be in south central NC, like me, I'm just north of Charlotte.
If your going 12 x 16 for the coop, I would seriously consider a Woods coop. You will have great ventilation, light and a nice...