IMO it makes more sense to predatorproof the pen sides around the ends of the roosts than to try to keep the chcikens from roosting near the pen sides. Reason being, the former is very easy to do in a pretty 100%-foolproof way, whereas the latter may have a significantly nonzero failure rate (as chickens develop agility you had not expected <g>) which may lead to headless chickens in the morning.
All you need to do is take a piece of plywood or roof tin with holes drilled in a few places, or some hardwarecloth, and wire it very securely to the pen wall at the end of the roost. Ideally this would be done from the inside (makes it essentially impossible for predators to rip it off) which would mean removing the roost branch, drilling a hole in the center of your plywood/tin/wire/whatever, and then reinstalling the branch after the predator guard is on. If you wire it onto the OUTSIDE of the pen fence instead, you had better have great confidence in your ability to do so in a way that predators can't pry off. But it works really well. You can eyeball what size piece you need according to the size of your chickens. Err on the side of bigger rather than smaller.
Good luck, have fun,
Pat