So I built my coop thinking my biggest hens would be Black Australorps and Buff Orpingtons. My pop door opening was about 11" X 14", but after I trimmed it out it might be closer to 10 x 13. My golden retriever, George, could fit through the opening before the chickens moved in. Outside view Sliding panel on the inside I discovered one of my Australorps might be a Black Jersey Giant. The soles of her feet are bright yellow like a BJG, not the light grayish/ pinkish of the Australorps. I don't really know if she will get really big since she is from a hatchery. If she does turn out to be a BJG, will she still fit okay, or do I need to do some alterations before she outgrows the opening? It won't be easy to go back and fix, but I really like this chicken and don't want to get rid of her.