OK here is my problem my big coop was originally a 4x8 tack shed. Someone cut a chicken door in one corner and slapped in some shelves for nesting. I want to put exterior boxes on the backside. I will also be ripping out the shelves for roosting space. I've not done alot of construction (hubby says I'm on my own when it comes to the chickens) so I need to keep this as simple as possible. My question is what are the minimal dimensions for a nest box. I have standard size and bantam hens, nothing over say 6 lbs if that matters.