For a roost, I built a ladder-like structure off 2x4 with the rungs 18 inches apart leaning against the wall at a 45 or so degree angle. The rungs are about 48 inches long, the width of the coop. The chickens all crowd on the top rung. Go figure.
I built the nesting boxes into the wall of the coop so that the unit extends out. There are three nesting areas, divided from each other, with a opening roof for access. It is a couple of feet from the floor of the coop. The distance was what seemed to be comfortable for me to reach in to clean and remove eggs. There is a perch in front of the nesting boxes for the birds to fly or jump up to so they can walk into the boxes. I don't know the perch is necessary, but it seemed like a good idea at the time.
Chris