For chickens to nest they need 3 sides and a bottom, so a flat plywood bottom and dividers large enough for a hen to sit comfortably in some hay/straw. They also need to be up off the ground and in a safe place like a chicken house. I would use the sides to hold up the back. If you need the whole chicken roost and boxes, there are some great ones available. Here are some photos for you: https://www.amazon.com/s?k=how+to+build+chicken+nesting+box&hvadid=238244140272&hvdev=c&hvlocphy=1028471&hvnetw=s&hvpos=1t2&hvqmt=e&hvrand=1397168347856475079&hvtargid=kwd-393240909810&tag=googhydr-20&ref=pd_sl_636p8uyiqw_e
Any type of box will do. They should be 12 x 12 x 12 for regular chickens. Here is a website to help. https://www.thehappychickencoop.com/chicken-nesting-boxes/
chicken coop? pet chickens were the rage a while back, the county extension office had plans for building the coops. that's been a while ago. but...ask them.