Our coop is an open air coop, but it has a solid roof and a windbreak on the North wall. Last year we did this and only used one heat lamp. We used the deep-litter method which was easy until Spring Cleaning. It kept the drinking water, combs and wattles from freezing, and I even got eggs from time to time even though that was not my concern. I can live without eggs during their resting period, so long as they are healthy and happy. As long as your chickens are adults and are able to stay dry, you don't really need all that much heat even in freezing weather. (I know this is hard for those of us who baby our birds... believe me, it took my husband a very long time to convince me too.) My husband told me about a truck that turned over near their house. It was transporting chickens. The owners managed to catch all but one rooster. The rooster stayed on his family's ranch for the rest of his life. He roosted in an old Oak tree, and even lived through a blizzard. I guess it is possible for Texas blizzards to be warmer than say Colorado, but either way, I was impressed. Last year our coop roof leaked in 2 spots, but everyone was fine, so this year I'm not at all worried.