Insulation isn't really needed unless you are in a very cold artic envirment, it might be nice in the roof to keep the coop cooler in the summer...you wouldn't want just tin for example in the hot sun. Drafts are those places that let the breeze blow through intermitantly. So you do want the west and north sides pretty tight. You don't want huge differences in temp between the indoor and out. Every notice how people with a/c never go outside? If your house is very warm in winter it seems way too cold outside? And you can feel those drafts. Ventilation will allow a steady state of evaporation to occur, and as hot air rises it will carry moisture and fumes up and out the vents. You also don't want the chickens roostng directly under those vents, heads under a solid part of roof, not too high up. Make sense?