I live in Central PA and we have an A-frame tractor for our chickens. It is built with 2x4's and 7/16 plywood, is 8 feet tall and 8 feet long. Coop up top and run underneath. Our girls had no prolems in there this past winter. If they were cold, they went up, but most of the time they were in the run. We did put a light in the coop for some heat. Also, once we started getting large amounts of snow, we stapled some heavy ply plastic around the run, so they wouldn't get snow in there. That helped to keep some heat down there as well, not much, but a little.
ETA: Please don't think we had all of the chickens in my sig in that coop. We only had 6 hens last year, the rest have come this year. We build another A-frame and are in the process of building a banty house. Plus, some are still in the brooder.