Many of you have good questions concerning the number of nest boxes needed for the Playhouse coop. Most chicken people agree that one nest box can be shared by up to 5-6 layers. In the 4 x 8 and 4 x 6 version I specify only one nest box. For the 8 x 8 version, two boxes sit side by side and can be accessed by a single egg door. This works all fine and well until one of the hens goes "broody" This is when she wants to sit on her eggs, (in the nest box of course) day and night until they hatch. Thoughts on a broody hen can be found elsewhere on the web or in books.
The nest box is a cube framed with scraps of plywood and the framing members. construction is not critical. Size matters. I try to make sure that the overall dimensions are 12" x 12" x12". The photos in the plans should give you an adequate idea of how to construct it. In essence, think of making a cube of framing wood and plywood, , then removing two opposite sides of the plywood. One side allow the hens access, the other allows access to the egg collector. If the hens are not using the nest box and laying elsewhere, try making it a bit larger. A little straw in the bottom will also be needed.
If you are using a slide out plywood floor on the bottom of the roost box, then consider hanging the nest box a few inches off the floor and attaching it with screws to the wall of the roost box. This will allow the slide-out 1/4" plywood floor to slide under the nest box. When roosting, the birds tend to sit on the flat roof of the nest box and drop their droppings in the space between the roost box wall the nest box.