Working on our coop so that we can get our chicks outside, and need help with size. I've read that there should be a minimum of 4 square feet per chicken. We plan to keep 12 birds total, and they will only be in the coop at night, free ranging during the day. Does that change the minimum requirements? The coop will be mobile and it will be moved from pasture to pasture to follow behind cows. Thanks for any input!