My roosts are 2x4's, flat side up, about 12" apart and 12" from the wall. There are 3 roosts, built in a simple rectangle, around 4' x 6'. I didn't want roosts of different heights because I read they will compete for the high roost -- but many, many people offer more than one height, and I've had a couple of loners find a way to roost higher and by themselves. Birds' feet don't curl around something narrow like a broomstick very well, not to the extent other birds' feet do. I've read of really big Orp (or JG) type birds (like 12# up) using a small shelf. A 1x4 should be fine if it's short enough -- but if it's very long, it's liable to sag and maybe eventually break.
Many people also use branches -- but thick ones.
Mine are 30" above the ground, but 2' makes sense to me for a large bird. My coop is oversized, and they fly sideways off the roost, sometimes using up to 6' of space to the side. They can injure themselves if forced to fly down in a small space, so also consider this in your planning.
Another advantage of a flat roost is frostbite prevention, if you live where it gets well below freezing. By sitting on their feet, with no toes hanging off the edge, their feet are protected.
