My coop is tiny -- about 12 sq feet for 3 birds. It is attached to a covered run. It has no door at the top of the ramp to the coop -- just a chicken-sized. I've just been locking up the run at night. But the opening to the coop is just open all the time. The roosts are away from the opening. But, do I need a door for winter? Here in Seattle it rarely freezes -- maybe 10 days a year, maybe none. I'd say winter lows hover around 40. But, of course, it does get windy sometimes, and I'm sure there's a draft in there. What do you think?