Thank you everyone!!
No, Andy is not a carpenter, but he did used to work in construction. I think he's one of those guys who can just figure things like this out in his head. He didn't even have any plans and he's never built a chicken coop/run before - he just looked at some pictures and sketched out some very basic measurements - then built as he went. It's very amazing to me. I WISH I had his skills - then I'd be building a ton of stuff! LOL