I inadvertently did something like this over twenty years ago, with my first chickens. They came from a neighbor, who said they would "do just fine" roosting in my pole barn rafters. They were Belgian d"Uccle bantams, very good flyers. I fed them, and watched. Over several generations, the survivors were very cautious, leaner in body type, and loosing their foot feathering. I lost enthusiasm completely, and built a safe coop, and would never go back. Going out in the morning to body parts, piles of feathers, and severely injured but alive chickens. AWFUL! I'd rather watch the real wild birds, and take care of the chickens. Mary