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They're not hard and fast numbers... it's a matter of "some things are better than other things, but chickens will adapt to a lot of different situations although it may affect the degree of social friction in the flock".
How far off the ground: there is no minimum. Even if it is lying *on* the bedding, some chickens will still prefer a piece of 2x4 or whatever to just sitting on the bedding at night. (Others won't). I would suggest that ideally your lowest roost be either so low they can *easily* hop onto and over it, or high enough (like 18"+) that they can easily walk under it. But they will not curl up and die if that's not the case.
How mcuh space between each bar: depends on how much you want them to fight (if bars are parallel) or poo on each other (if it's a ladder type configuration, which I *think* is what you have in mind here?). I would not go less than 18" horizontal separation if the space is available, but that is not to say that *some* flocks can't get along peaceably with less.
You seem to be planning on a ladder-style tiered roost? That is not necessarily always the best arrangement in all coops, so make sure you've thought through the pros and cons of the alternatives.
How much roosting space per chicken: I'd plan on 12" linear roost space per chicken for normal-sized breeds, but most of the time they will snuggle together and leave a lot of roost unoccupied. From a space-packing point of view, they only need 6-8" apiece. However it is really much wiser to have a generous amoutn of roost because it allows them to not get along with each other in peace, you know? As opposed to causing or exacerbating pecking problems.
Good luck, have fun,
Pat