As to coop size,
that is another highly debated topic.
Though really... The suze of the coop I guess means nothing... Because maybe you have a tiny coop with one chicken, or a giant coop withh 100 crammed in... It is really a matter of number of square feet per bird. And that
is a highly debated topic,especially where it gets very cold -30 etc.
Some say you need a small number of square feet per bird, or the birds will freeze.. Like 2 square feet per bird.
Others say that 2 is much too small, too many cannibal issues will crop up.. You need 4 square feet, but not more than that, again because the birds will get too cold.
I vote for a MINIMUM of 8 square feet per bird, of covered wind free and snow free space.