In my continuing research about raising chickens this is what I have learned so far.
Interior floor space: A minimum of 4 square feet per chicken of interior floor space. This doesn't count the nesting boxes.
Interior air space: Chickens need to roost at least 30 inches up off of the ground, and have head space to do that comfortably.
Roosts: They recommend 6 inches per hen. Rounded roosts are the best because hens have special ligaments in their legs that lock in place when they sleep. This is how they can sleep without falling off the perch. To do this, they need to be on a round roost. It is best to have roosts at varying heights which helps with flock dynamics.
Windows: Sunlight is essential in a coop. Hens have very poor night vision. Even if it’s daylight outside, if it’s dark in the coop, your chickens won’t get moving, eating, or laying their eggs if they can’t see to hop off of the roost. Also, sunshine is a natural sanitizer. And, the hens appreciate a sunny spot on a damp and cold day to sit in. Finally, windows allow you to look in, and sometimes you need to know what’s going on in the henhouse!
Ventilation: Soffits in the eaves are important. Also Windows that open when it is hot are a necessity. Another option is a cupola because it is very effective in pulling damp air up and out.
Nesting boxes: Plan on 2 or 3 for seven or fewer hens. For a large flock have 1 box for every 5 birds. These can be homemade or purchased. Mine are built on the outside of the coop.
Exterior space or Run space: Should have at least 8 square feet per bird for the fenced run.
Flooring: You can have anything from dirt to wood to concrete. If you do have a dirt floor, then make sure that you can protect your hens from digging predators with underground fencing. If you have wood, you can add a sheet of inexpensive vinyl to keep it from absorbing moisture and to ease cleaning.