Hey! Ihave several tractor coops, sized 4x12, with 2x4 framing, the four foot heigth matches the heavy 1x2 mesh wire it is wrapped with, with 1 inch chicken wire over the top. A low nest box House with about 16 inches above the ground, and at least 3x4, in dimension gives up to 20 birds room to run and avoid bickering. The nest house is about 4x3 or 4x4, and has a ladder from the yard, a chicken nipple system for water, and a tray for feed. Theoretically, 4 x 8 should handle 4-6 birds easily, but I burn out the grass with their scatching and hunting, so we move the pens, every coupla days or so. In reality, it depends on your birds, whether there is eough wing space. Some aggresive breeds will bicker for space constantly. others, are quiet, as long as there is ample food and water. We have Appenzellors, that are not supposed to do well confined. They just cackle about, and call when they see us without apparent stress in the flock. (If free ranged they will roost in the trees at sundown and not retutn to the coop. We removed a Fox to another location, last week, but that does not make the grounds predator free).
My last pen is 3/4 PVC hoops on a heavy frame, 4 x 12, with chicken wire and a tarp covering the front. inspired by a lister here, we decorated the front like a Western false front building, and named it Chicken City, for a former dining chain, and because it was built to grow out some 20 X-rocks for Freezerville. It gets attention from the road, and will support the EGG sign, out there.
We have caging, from rabbit run size to 6 x 5 houses with 50 ft of wire surrounding an open top yard.. The chickens enjoy the outdoors, but the shade under the houses too, and usually will shelter under the house rather than in it.