I'm building a small coop for 3 Bantams tomorrow. It is 4' by 4' by 4' with a small run the same size. The run is on the south side of the coop, the people access door is on the west side of the coop. Where do I need to put my ventilation and what size do I need? It will have a flat slanted roof which drains rain from south to north. Thanks for your assistance.