There's nothing magical about using dimensional lumber for roosts! Chickens are designed to roost in trees, actually, and do very well on branches or saplings, 2" to 4" diameter, bark on.
Don't use metal or plastic, or very smooth dowels.
In winter the birds cover their feet on those saplings too.
Here we have multiple choices for our 40+ overwintering chickens, who range from bantams to big birds. Their roosts range from 2" to 3" diameter saplings, to 4" diameter fence posts in the old coop as rafters. There's also an old split rail, with smooth edges, and a few birds like the 2"x 6" rafters in the newer coop section, 9' up.
It's about their social status more than anything else.
If all you have is lumber, that's okay too, but it's certainly not necessary to use it.
Mary