Sticking with common dimensional lumber sizes as a starting point for designing a coop is time saving straightforward. We have had 20 chickens in 64 square feet of coop + external run with great success. Even when they are stuck inside coop because of weather, they are all happy and healthy.Following with great interest! Seems to me going 4'x8' is a smart choice. I'd like to have one that holds minimum 20 hens and I'm looking for designs based on 4x8... maybe it'll need to be 8x8..not sure. Thanks for your ongoing updates.
Some would disagree, but 10 chickens per 4x8 sheet of plywood is where I’ve settled for coop floor size. There is also effectively more square feet once you build any platforms or roosting bars in the space as well.