When I built my first coop where I am at near Billings, I made a pole style building (my dad had a bunch of lodgepoles laying around) and then sandwiched styrafoam in the walls for insulation. Ventilation us on the north and south sides, and the window is an old recycled storm window from my dad's family homestead. If you use insulation, make sure it is well sealed up, because chickens love eating styrafoam and will get into the fiberglass. Old newspaper, straw, and other things like that can invite mice, but can work too.