I have a 10x12 coop with 20 pullets, different breeds and 15 bantams, different breeds. They only stay in the coop at night. I have a free range pasture that they stay in during the day. I use a deep litter system, and so far it is working fine for me. I plan to seperate the bantams from the layers this spring, and put the layers in the barn and a different pasture. They don't make much of a mess if they stay outside most of the time. If we have a cold, rainy spell I have to clean up more often. Keeping more birds in the coop keeps them warmer in the winter. The coop is well ventilated and has plenty of roosts for the different breeds. I would not keep that many in the coop unless they couldn't be outside most of the time.