Our built our barn specifically as a chicken barn. It is 20x24 and has two lofts to hold 20 bales of straw, brooding equipment, spare feeders, etc. The eaves are wide open at the bottom, allowing the flow of air to provide maxium ventilation. The upper eave, also wide open, is where the air exhausts, carrying humidity and fumes with it. Of course, such an arrangement also means the barn is not heated in any way. Nor is it insulated. We live in northern Michigan, where winter lows dip to -20F and -30F with regularity. The chickens do just fine.
There are grandkids in a lot of my photos. Sharing the joys of rural life and chickens with the kids is on of my special joys.