It's really hard to say just what you will need to do for ventilation, observation is best. I keep a thermometer in coop. Go out into coop during severe weather(rain, wind, and snow) and see how the air is moving around in there and if there's any rain infiltration, you should be able to see any trouble spots and modify them.If I put my roost in the southwest corner, would I ever really need to close up the windows during the winter? There are vents in the eaves continuously around the edge - like house vents.