I’ve had several people ask about housing and caring for hens in winter, and it’s best to start thinking about it now while the weather still allows for easy modification of the coop.
People are often shocked to find out that coops in Michigan don’t need to be heated. They do, however, require adequate ventilation- in cold temps, the breath & waste from chickens create a damp environment in ventilation restricted coops, which can lead to condensation, frostbite, and ammonia buildup.
A good example of a coop suitable for Michigan’s winters is located here:
Robert Plamondon has a thorough write up regarding proper winter care on his website: