Oh, what could have been. I'll mention this any way since you are building new coop. With corrugated roofing like that if you leave the ends open to the coop you get a lot of ventilation because of those openings. Or if you don't bring your siding all the way to the top under the overhangs you get great weather protected ventilation. It depends some on how you frame it. You need to cover the opening with hardware cloth for predator protection. This photo might give you some ideas.
For getting through this winter with only four chickens listen to the others. You should be OK.
For getting through this winter with only four chickens listen to the others. You should be OK.