My chicken run / hooch is about 4' x 12' with 2x2 wire for the walls. The actual hooch is made from plywood and is off the ground so I don't think I have a problem in their, but every once in a while I do have broken eggs.
The floor is dirt, and on the outside I have the 2x2 wire going out about a foot. They seem to dig under the wire as apposed to going through the wire. I keep finding tunnels and them I will fill them with rocks or something to block them up. I would be very hard to cove the entire floor with wire. It's a big coop with a roof and I would guess it weighs a few hundred pounds.
I know that over all getting rid of the rats would be best, But I live on a "Green Built" that is brush and lots of water so I don't think that is possible over all. I also don't want to use poison because the chickens may eat it.
I am at a loss oh how to deal with these buggers so any suggestions would be GREATLY appreciated. No other pest problems, in fact most of the time the chickens come and go in the yard as they want. Although I am building a fenced enclosure that is 10' x 60' to keep them looked up in. Getting tired of the poo all over the place. :)