Parront
Crossing the Road
This is the best way to tell the weight/over weight status of all birds. A "sharp" feeling bone = too thin. Dull blunt =OK, but can't feel a bone, or a dimple, = a fat bird, which is what the Cornish-X are bred to be!I think feeling the keel bone would be the best way to tell if they are eating right. If it is very prominent and you can pinch it without feeling anything around it, they are too thin. If there is a lot of fat surrounding the keel, they are overweight. There should be a thin layer of fat around the keel, but you should be able to easily feel the keel bone.
For coop design, nothing special. You might want to include a low roost in case they want to roost, but have thick bedding so they can sleep on the ground if they choose.