I am converting an old horse stall (in a metal pole barn) into the winter chicken coop. It is 12x12, tongue and groove 4 ft up on two sides and 8 ft on the other two. I plan to put on a plywood roof, wire over the two open sides and a few heat lamps up. Do I need plywood sides over the open rails? How warm do chickens need to be in the winter? We live in Central Illinois, so it will be pretty cold. Thanks in advance!