I live in Michigan, I would not recommend an open air coop. This winter so far has not been as bad as usual, but still pretty cold. Despite my best efforts, my Roo got a little frostbite.
Be sure the check out the Michigan thread, lots of friendly folks to help you out. https://www.backyardchickens.com/forum/viewtopic.php?pid=3491750#p3491750