I use two, one in the coop "just in case" and one in the pen. The feeder in the coop is one of those galvanized metal, finger-slicing tray type things, and it's just there in case I get stuck someplace overnight (work issues) and can't get back to let everybody out for a day or two.
In the pen, I hang a 3-lb plastic feeder at "chicken back height" which they mostly don't spill out onto the ground. It's more likely that *I* will spill feed as I fill it.... Because it's hung from a spot half covered by solid wood, attached to hardware cloth over the other part of the pen, rain was getting into the feeder from the wire side of the secured pen.
So I meandered through the local Goodwill store looking for pie tins (I'm not a cook, don't have stuff like that at home) but found a round, plastic thingie which sorta looked like a round cake pan. I snatched that up for 49 cents, took it home, cut a hole in the middle and made an "umbrella" cover for the feeder, sliding it down the wire hanger to the top of the unit. Just have to tilt it up to fill the feeder.
It SEEMS to work well. As I said, most of the feed spillage appears to be my fault. But I am only feeding 7 chickens.
WHEN I add to the flock - sooner than later, I fear - I'll probably try to build one of those wooden gravity feeders after felidaet's design.