We had a large raised box garden in our chicken yard. Since there was no chance of growing anything in it, thanks to the chickens, we decided to convert it into a small coop with its own integrated run in case we needed to separate a hen, introduce some new chickens, or let our Buff Orpington raise some chicks when she goes broody.
The raised bed is 4' x 9'. The sleeping area is 2' x 4' at one end of the raised bed, the balance of the bed is enclosed and covered.
We introduced some new pullets to our flock by letting them live in the mini-coop for a couple of weeks before releasing them into the large yard with the rest of the hens. It worked really well.
My husband added a door/ramp to one side so that the pullets could spend the day out in the big yard and then return to their little coop at night. We did that for a couple of weeks after their first two weeks living exclusively in the mini coop. Now they are sleeping in the big coop with the big girls.