Range Feeder for Chickens

Recently constructed this basic range feeder so that I could feed the chickens out in our rather large secondary run. The main base is 28" x 16". The hopper is large enough for two 40 lbs bags of layer pellets. The top hinges for easy filling:



We get a lot of rain here in Copalis Beach, WA so the overhang on the roof is fairly substantial and I've mounted the entire unit on some concrete pavers to keep it out of the muck.

Any thoughts on how to improve the design. I need to make another similar unit for the Turkeys. The only problem I'm noticing is that the chickens are roosting on top of the roof of the feeder and starting to poop all over it. Any ideas on how to prevent this? I was thinking about making something like they put up to stop pigeons from roosting in the cities, the wire anti-roost things you see at some airports.