You need insulation and ventilation.
I designed mine so I had two windows, one door, a pop door, five vents, a secluded roost and a nest box. I have no idea what it cost -- numbers that big frighten me.
The feed is on a shelf held on with magnets. The water is on stepping stones in the corner by the pop door -- initially I thought it would be suspended from the ceiling till I realized that would result in more of a swinging sprinkler. The nest box originally had two sections divided into two nests -- the divider designed to me removable if necessary. I am glad I did this as I just hatched chickens in there and they need the room.
I am real happy with this design. We built it from the inside walls out. It is insulated with foam. (Slice foam with a knife heated with a blow torch and it cuts like butter!) The floor, sheet linoleum, went down first, walls screwed right onto the floor. This made laying the floor super easy AND nothing will get under it from the inside. This coop kept them warm all winter (I suspended a heater from the ceiling.) It keeps them cool in the summer. Where the heater was, I have now suspended a fan. When the heat is 95 outside, it is 77 inside.
Also, the vents are closeable, which I did in winter when temps got down to single digits.
I hope this gives you some ideas. We bought materials a bit at a time. Every few weeks I emptied my pockets and bought more materials. Doing it that way it took a little more than two months to build.
