For nest boxes that also work well for incubation purposes make each nest free standing 12 inches wide (11 & 1/4 inches wide using a 12 by board) 12 inches tall, and 24" deep with a two inch gap between the roof and sides. let the top or roof overlay the sides & rear walls 3 inches on 2 sides and on the back end. This results in an extremely private nest that hens search out because it offers them safety as well as seclusion. Also a nest with a low roof will not get scratched out as much as a tall nest.