I've had a hard time convincing most folks on BYC of this, but there actually is a scientifically studied correct roost design......(a 2 x 2 with top edges eased)....
https://www.backyardchickens.com/threads/proper-design-of-roost-bars.1197058/
These modern era guys came to the same conclusion as poultry science researchers did 100 years ago.
BTW, as per some of the humane society bunch that cares about animal welfare, etc. one of their requirements is also a perch of this same type of design. They call them perches....not roosts......but theory is the same. Birds as supposed to be able to grasp the perch with both front and back toes......not just balance on a wide board as they do with 2 x 4's, wide side up.
https://www.backyardchickens.com/threads/proper-design-of-roost-bars.1197058/
These modern era guys came to the same conclusion as poultry science researchers did 100 years ago.
BTW, as per some of the humane society bunch that cares about animal welfare, etc. one of their requirements is also a perch of this same type of design. They call them perches....not roosts......but theory is the same. Birds as supposed to be able to grasp the perch with both front and back toes......not just balance on a wide board as they do with 2 x 4's, wide side up.