For some reason the topic of what to use for roosts stirs up a lot of people on this forum. Some people get emotional over what they think is best. I’ve never quite understood that. Like a lot of things concerning chickens, one way is not necessarily right and everything else wrong. It’s usually just which way we choose to go.
As you can see by the responses, the reality is that different people use different things that work well. I do suggest it be wood. Plastic or metal can be pretty slick and wood works better than metal or plastic in the cold as far as heat transfer. And what you use needs to be strong enough to support their weight.
If you use sawed lumber, I suggest you sand it a bit. Part of that is to round off the sharp corners but my main reason is to get rid of splinters. Again, that is just personal preference. The chickens generally don't care about most of this type of stuff. People do.