You'll need a roost, or roosts, nesting boxes eventually and possibly a place for food and water. I keep water in the coop at night, but the food comes inside with me. You'll want 3-4 sq. ft. per bird, depending on your weather outlook. I don't foresee a time when mine will have to stay in all day, so I cheat a little on space and omit feeder space. One really important thing to keep in mind is ease of cleaning. I let someone who doesn't do the cleaning design and build my big coop and it's next to impossible to clean. The plywood floor has numerous gaps that trap bedding and poo and I have to get on a ladder and contort my body to get inside and clean. The doors all have a little lip of plywood at the bottom that prevents me merely sweeping it out. That was more of what you don't need than what you do need, but someone should benefit from my mistake.
