I recently read an article from a link here on BYC on a coop design from waaay back in the day, early 1900's with one wall completely open, even in winter. It was covered with chicken wire for safety but no walls or windows to close off the weather. The article stated that even with the cold weather, the idea of the fresh air was so much more beneficial than either heating the coop or closing it off to keep in heat. My coop is a solid building but I have windows on the east and west sides and the roof is pitched towards the south with some of the opaque plastic roofing material to let in more natural light. I am planning on keeping the window open this year that faces the east. I live in SW Ohio and most of the bad weather we get comes from the west. The west facing window will be covered with plexi-glass so they will still have afternoon light coming in, but I'm going to leave the east facing window open, only covered by 1/2" hardware cloth. I am going to go with lighting the coop on a timer for egg production, but will not have any heat, I know there is a risk of some frostbitten combs but my chickens aren't show birds by any means, I have about 20 hens and 3 roosters (1 too many roosters if anyone's interested in a gorgeous Americana rooster let me know) Any thoughts about the open air coop are welcome.