Auto feeders, as in bulk feeders like the Little Giant type? That would be the draw for the rats. Get a good rat proof treadle feeder with a heavy counterweight and a spring loaded door, install it according to the directions (no getting inventive!), and train the birds according to the instructions and the rats will leave. You need full size birds or at least some, not meant for an all bantam or all silky flock.
Removing the feed at night is gonna get old fast and you are tied to the coop twice per day. Water, unless you are in an arid climate the water alone won't hold rodents there. Rodents almost always live within a few dozen yard of their food source and natural food sources will limit the rat population. Traveling and foraging for food is also very dangerous for a rodent. The only time their population can explode is when a human is leaving food available be it a coop, trash bins, or a warehouse with edibles.
Do a forum search on rats and chickens, there are dozens and dozens of threads covering dealing with rats. Howard E.'s post on Rats 101 is excellent. But all you really have to do is be responsible with the feed, responsible for basic sanitation to prevent other food sources (compost), and rats cannot live in a chicken coop. They will leave when they get hungry.
