I plan on building a triangle shaped tractor with one end of the tractor being thier coop at night. What size does the coop need to be for 6 barred rocks? I now the rule is 4sqft per hen, so 16sqft, but is that the same if it will only be there house at night? Otherwise they will be in the tractor during the day. I'm trying to build something that has enough room but can still be moved.