You can put them as high as you want as long as their are other roosts lower that they can walk on to the highest one (chickens prefer to roost high) but they need a way to get there so you could make a ladder up
For standard size breeds, I've found these specifications to work well for roost bars in the coop:
* At least 1 linear foot of roost space per bird
* Roosts at least 15-18 inches from walls (to reduce poo on walls)
* Roosts at same height or everyone fights to use the highest roost bar
* Roosts 20-24 inches apart so chickens cannot reach over to pick on each other
* Roost bars no higher than 2 to 2 1/2 feet off the coop floor to reduce foot/leg stress when birds jump down off the roost
* Roost bars no closer to the coop ceiling than 2 feet to reduce moisture collection (and frostbite) on combs and wattles during winter
* Roost bars in discrete, separate areas of the coop so birds can space themselves to reduce stress. Multiple, spaced roost bars have worked much better than 1 continuous roost bar, especially for a flock with roosters, laying hens, and juveniles.
* Roost bars of untreated, unpainted pine 2 x 4's with either flat or narrow side up
* Roost bars (2x4's) sanded on all 4 edges for foot comfort
* Roost bars inserted into fence post brackets so they can easily be removed for cleaning (fence post brackets are about 69 cents apiece at Lowes or Home Depot)
* Roost bars higher than nest boxes, so they're less tempted to roost on or in nest boxes
* Roost bars positioned away from feeding, watering and nesting areas of the coop so chicken poo does not drop into these areas.
I don't have roost bars in the runs, so I can't help you on that one.
I use tree branches that have been bark skinned, I feel they are more comfortable for the chook's feet because they are round. If they get too messy, they can be tossed and cut them some new fresh ones. I have two full width of the coop shelves, one above the other, against the back wall, on which are my nest boxes. Above the highest shelf I have suspended just the rungs part of an old wooden ladder. This does not hang over the shelf but is forward of it about center of the coop. I only have a dozen hens so there is no fighting for space. I have a chook ladder from the floor to the highest shelf, against the far left wall. The feed and water are not anywhere that can be pooped on from either the shelves or perches. That's the set up inside my coop which is 8' x 10' plus their outside covered run.