Probably the lowest intelligence level of every breed i've tried, These are always the first to go when predators are hungry. Would fine if in safe confinement with Arial predator protection.
I would either - charge them for the whole bird or just not sell to them at all. Its tough as small operation , especially if your not processing birds yourself .
for the door ---- I used the grooves on old tongue and groove flooring I capture from a building being demolished and added plywood that slides in the grooves .
I leave alot of venting , and then cover the coop with greenhouse plastic in the winter . If you notice my walls are open on the ends along openings on 3 sides , but i left 1 wall completey solid so i can turn it into the wind in the event of cold night or severe weather .