I have the coop ventilation positioned so that it's not in the way of the coldest winter storms, which are southerlies in my area. The south wall is solid, so I can ventilate even on horrible days without wind blowing through. I also have a series of plastic "curtains" on the run that I can roll up or down depending on the weather, just to protect them from the worst of the bad weather. Inside the coop, the nest boxes are in a line along the middle of the coop but facing away from the door for privacy. The roost is behind that, so even though the coop door is open to the elements, they won't be drafty where they sleep (although they prefer sleeping in nestboxes). From the reading I've done, chickens are pretty good with cold, but they don't do well with damp or drafts. My coop shouldn't have those issues, but this is the first winter so I'll be keeping a close eye on things.