I made nest boxes out of square milk crates, and just leave them on the floor, in the corners of the coop. I put the boxes on their sides to make an enclosed cubby for the hens to walk into, and fill them about a third full with dry hay (making a little dent in the center). I also keep a fake egg in each nest for "encouragement". (I use a "hatching turtle egg" toy that looks and feels identical to the real thing!)
At first, the girls were pulling too much hay out of the boxes, so I then added a small "lip" to the front of each box, to help keep the hay inside the nest. I simply cut some wide strips of hardware cloth, bent them into shape so they would wrap slightly around the bottom and sides, and zip-tied them in place with wire ties. (Don't leave any sharp edges at the top where the chickens will be stepping over and could cut themselves.) This seems to be working out well, although all three hens tend to lay in the same box most of the time. I have occasionally seen a hen use the "backup box", possibly when their first choice was already occupied. I'm glad that I have extra boxes around, to prevent squabbles and so each hen could have the opportunity to go broody if the need arises.
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We have a very large coop made from a 10' x 10' shed, that was originally built for housing peafowl. When we lost all five of our peas last spring, my oldest son decided he didn't want the added responsibility of raising peafowl for the 4-H, afterall. So we now use it for my younger son's Blue Orpington chickens. They have a very long, attached run with an enclosed top (originally to keep in flying peafowl, but now serves as great predator-proofing).
I had to separate the Blue Andalusians from the larger Orps, however, so they're now living in a "temporary" makeshift coop, made out of an old gazebo-shaped rabbit hutch, lattice fencing, and a blue tarp. We really need to build them something more permanent and weather-resistant soon, before winter hits! If we can't rehouse them in time, I will need to cover some of the open areas with plastic sheeting and add a heat lamp somehow. Either that, or perhaps I could move their "hutch coop" inside the "shed coop" for warmth, and then carry the lone roo and hen in and out to their separate run, each morning and night. That shouldn't
totally disrupt the social sanctity of the separate breeds, I guess.