Ours is currently 12x12 with 8 foot to eaves and they all overhang 6 inches and are enclosed with hardware cloth to allow ventilation but prevent predators.
The windows you see in the pictures are currently closed off with insulation for winter. All windows are covered with expanded metal for predators also.
The first 3 feet when you walk in is the 'people area', although right now it's the broody area! There's broody nests on either end with chick sized feeders and waterers, currently there are 3 broodies with 8 chicks and one broody on 11 eggs in residence.
There is a full width chicken wire wall then with 2 doors. The main part of the coop can be divided into two parts by hanging panels if needed.
The doors are about 8 inches off of the floor to allow humans to step in but make it harder for birds to scoot through. From door down we also put a finer mesh wire to prevent chicks from scooting from one area to the other and possibly getting separated from their mama.
The main coop has numerous sand shelves at different levels with ramps to allow for easy movement. The front edges of the shelves have quarter round molding on them to make it easier on the birds to grip them.
We have an additional broody area in the main coop, Dillon is leaning on it here.
Nest boxes are scattered around, the blue treasure chests were found at Walmart for $5 and the birds really like them...
Nest boxes can be homemade (notice our 2 over 2 wood ones that the cat carrier is on) store bought or repurposed containers ranging from 5 gallon buckets to pet carriers.
As you can see we use sand on the floor and shelves...we sift it to clean and add ashes and PDZ when needed.