I created a nesting box from a bookshelf we had saved from the trash pile! I think it turned out pretty good. I want to add a small perch in front of it, but will wait till it's mounted before I do that. I might want to wait until they are supposed to get up in it, so they don't decide they want to sleep in them before they start laying.
This is the shelving unit that I started with.
This is the end result of a nesting box. I will be adding a slanted "roof" to it once it's mounted as well to keep them from perching and laying on top of it. I left the slats open on the top to help with ventilation and am considering adding some curtains for the box since it will be in a highly lit greenhouse/coop. Gotta give the girls a bit of privacy.