The nest boxes ARE for laying eggs, actually. Until this or that hen goes broody in one....
I wouldn't have roost bars higher than four or five feet, for the exact reason citychix mentions. I happen to have an old 3-walled carport/garage building transmorgrified into a large coop with four walls (17 X 20 feet); the flock has two ladder-type roosts with four roost bars apiece, each about 18 inches higher and slightly back.... Think a really, really wide ladder leaned at a low angle against the walls. My Orpington ladies will roost on the highest bar, but hop down to each lower bar until they are only about a foot off the ground.
The old garage has rafters, and several of my less "fluffy" ladies fly up there to roost at night. Not many of the heavier breeds of chicken will fly at all (that is, higher than a foot or further than four feet) so they hop up the ladder roost rungs to get to the highest rung. My Orp hens have a lot of status in the flock, so the top rungs belong to them and my dominant rooster.
Hope this helps!