Welcome Bob from across the river. I just built a similar coop but just used kiln dried standard 2x4's on top of an existing cement pad that was an unused kennel. I used cheap ply wood and clear plastic corragated roofing sheets. My coop is uninsultaed and my little flock of 7 seem no worse for wear. During our last cold spell it got down to 9F here in portland and they were happy as clams. They seemed more miserable when it warmed up a bit and started pooring rain. I added a seedling warming mat between two pieces of ply wood and put a waterer on it so they had unforzen water. I have mostly winter hardy breeds but two a Houdan and a Polish are not and faired well. My Barred rock and EE never stopped laying, and only started in late Oct. So they are very cold hardy animals just as long as they have a draft free place to spend the night.