On the roost height, I was told 2 ft for large birds by a respected friend and breeder of oriental fowl.
My large fowl malay will roost on top of a 55 gallon drum (if I allowed it) and just jump straight down, babies included. I took the barrel out as it was only in the pen for egg laying/brooding purposes. I was afraid the young ones would eventually hurt a leg as it's usually my luck. I think what they liked was the flat surface to fully lay on that supports their weight without stressing their legs, as others have mentioned their birds used a table or shelf instead of the roost. Just an observation, not sure if that's really the key or not.
I've not seen the males try to fly at all. The females will, only to get up in a tree or down from roosting in said tree. And, really it's not so much a tree as an over grown bush...