I just spent the weekend lowering the roost in my coop, which involved building new nest boxes since the roost and poop board were on top of the boxes--quite a project for a "re-do." I lowered the roost for two reasons: 1) my big, fluffy buff orpington was having trouble jumping down from the roost in the morning--not necessarily because it was too high but because the coop itself is not deep enough for her to fly out a ways and land "gently." I was worried she was going to mash her beak on the front wall one of these days and 2) another of my chickens got injured (long story). She's doing great, but during her convalescence I realized that they are all going to get old one of these days. So, I decided that 24" off the ground is better than 36". As far as I can tell, the girls have no idea that anything changed--though my buff orpington may think she's a spring chicken!
Good luck!
Good luck!