There's a lot of information about roost choices, and it's true that PVC or metal are very poor choices, so don't use either!
When it comes to wood, it's interesting what's on these sites.
Remember that chickens were originally jungle animals who roosted in trees, not flat boards. They are designed to grasp tree limbs! If you don't have access to saplings or branches in the 2" to 4" diameter range, then substituting boards makes some sense, but is it the best? Not really, and the birds aren't warmer on that board in winter either.
I have saplings, a split rail from an old fence, and 4" fence posts as rafters in my old coop section, and the flock uses all of these choices, deciding based on each bird's social standing and flight abilities.
Also, set your roost bars so that they can be easily moved when you need to get under them!
When mites or lice arrive, spraying the coop and all roosts with permethrin is the answer! You may never see them, or fight every year, it just depends.
Mary