I cannot tell you what's right or wrong but as a novice will tell u of my recent experience. I went from 5 adopted hens and a rosecomb rooster to having 30 plus chickens in 2 coops and some free ranging the back yard in two months time. This morning, after I corralled all the 16 older chicks into their coop/run, I went in there determined to build them a roost. I had an old cedar post about 10 feet long and about 4 inches in diameter. I attached one end about 2 feet off the ground at the door frame and before I got the other end lifted in place I had chickens all over it. I think, because its round, they can get a grip on it. Just sayin.
I've read about using round roosts too, makes since to me!