Why not start with an IBC and cut a hole for the door? You could build closed laying boxes into it, and something for the chickens to roost on. Put some straw or saw dust on the floor. You could add vents to the side for air. If it sat inside a chicken run that you can walk into, the chickens could be safe, dry and happy. I have an extra IBC. Maybe this could be my chicken house? I bet I could even plant the outside of it with mud and grass for extra insulation and good looks.