Chickens will roost as high as you let them. They don't think about coming down the next morning. They think about getting as high as possible at night to be safe.
None of my roosts are higher than three feet tall. Most are more like eighteen inches. Larger breeds can injure their feet, wings, breastbones and evven break their necks comign down from eight feet high roosts. Bumblefoot, as someone else said, can can be caused by repeated bruising on the bottoms of the feet from hitting a hard surface every time they come down from a perch. Since the damage is from the inside bones and inside pad of the feet, you can't even tell by looking at your birds feet every day, until it is too late. By the time the sole of their feet goes necrotic, there is often already bone damage to the end of the tarsal bones, the cartilage is shot, and infection has set in and they don't make it. Bubmlefoot surgery doesn't help. Epsom salts won't help. Posting on here won't help. Neo-Tricide won't help. Better to just remove a few roost bars now, than have heartache later. Sorry for such a downer post. My friend had Jersey Giants and had to learn the hard way. Just sharing my experience with her, trying to save her best birds after an "I told you so." discussion about perches. Hers were built for her by a Hispanic man that raised game birds. They were fine for his breed. I told her they were not fine for larger, heavier breeds, but she left them up. Lost nearly half her flock to bumblefoot before she lowered her perches and put down shavings. Some people have to learn the hard way I guess.