Size
The size that works best is 12 inches deep, 12 inches wide, and 12 inches tall on the the side that connects to the inside of the chicken coop.
Sloping Top
The nesting boxes should have a sloping top. It should slope down to end up just below the roosting perch.
Amount
You should provide one nesting box for about every four hens.
Perches
You should alos provide roosting perches for the hens to sit on.
Material
You can use exterior grade plywood or plastic. Plastic chicken nesting boxes are gaining in popularity due to their ability to last longer.