I have a 12x12 inside pen attached to a 12x12 outside pen. I have 6 roos and 14 hens all together. I have pen of young from 2 months to 4 months all together and all my younger ones are mixed with other baby chick breeds.
It's not a stupid question. You learned something just by asking. That was actually a good question. I had a wooden box that was 2'x2'x6' that they slept & laid in. This was inside of a 8'x16' open air pen. I had 6 hens & 3 roos together & they raised young ones just fine.
Shoooot! with that big of a stall you could house a lot of breeding pairs, trios and even quads. Seramas are wonderfully small and you can get tons of nifty ideas here.
Rabbit cages sound great or make your own with J clips and hardware cloth. Stack them as high as you are comfortable with and put them almost to the ground.