Mine are 30" with no ladder, but they have about 8' of space to the side to "fly" down, which makes for a softer landing. If you make them really high, which they like, they can injure themselves if they have to jump straight down -- or if they won't use a ladder or ramp. Some people make them all the same height, some prefer the ladder style. I don't know that either is better. I do feel chickens are more comfortable with a wide roost, because chickens' feet don't curl around a narrow pole the way many birds' feet do. Mine are the wide side of a 2x4; a fat branch works just as well. Don't make them out of somethng like PVC pipe that is slippery. Roosts need to be higher than nest boxes or they will want to sleep in the nests, as they like to sleep as high as they can.
A poop board is something designed to catch the night's poop and make it easy to scrape it off for removal from the coop.
