They should have roosts. Mine are set up @ 24" with bedding, and I have never had a problem. Somewhere between 16" and 24" should be fine. A 2" x 4" or 2" x 3" with the corners rounded off make good roosts for big birds.
I've lowered some of my roosts and it sure makes bedtime go more smoothly. The hatchery birds like to be up high, the Delawares not so much. We're shifting things around this year so the facilities are more tailored to the bigger birds. It seems there's always tweaking to do.