The bars are rather low and look a little narrow as well. I have my roost sitting about 2' off the ground - you don't have to go that high but they'll naturally want to get as high as they can. You look like you have some vertical space so try lifting them to 18" if possible. For the bars, you can use a 2x4 (mounted either way, some people have the narrow edge up, some wide) or large branches - the one I'm using is about 3" diameter tapering to 2.5".