I'm new to chickens,and am reading about how much room is needed per bird inside and out. I also read about birds not leaving the coop in the winter, does this happen? I live in Michigan, we get lots of snow, cold temps, wind. If I build my coop to house x number of birds, and fill it, it's going to be pretty crowded if they spend the winter in there. Maybe I should build it alittle bigger.