What are your plans for the Brahma? Are you raising them to a certain age to butcher or will they be old enough and have girls in with them to lay eggs?
Chickens tend to like to sleep at the highest spot available. If your nests are higher than anything else, like roosts, they are likely to sleep in them and you will get poopy eggs. So if eggs will be involved you'll need roosts higher than the nests. If there are no eggs involved don't build nests and keep your roosts pretty low.
Cornish X and to a lesser degree the Rangers can get pretty heavy. They grow so fast that their skeletons often cannot keep up with weight gain. They can hurt themselves by jumping down from roosts, so if you put in any roosts they should be just a few inches high.
Brahma are big chickens but not in the sense of CX or Rangers. They tend to grow a lot slower so the skeleton can pretty well keep up. Brahma can fly. If you feed them in a way they get heavy for their age and size you can have issues. Usually you don't. If hens laying eggs are involved and you have Brahma's I'd want the nests fairly low and the roosts reasonably low. If no eggs are involved then keep the roosts pretty low. The highest thing available doesn't have to be that high.
