We have two coops, both raised. The 8' by 12' coop is about 18" to 24" off the ground. We did this for a variety of reasons, uneven ground, rot prevention, and vermin avoidance. We put chicken wire over the floor joists before attaching the plywood sheeting. It won't stop them, but will make it less fun to chew through.
We have hardware cloth over the window openings and vents, plus a tight fitting human door. Our pop door is heavy 3/4" plastic like that used for cutting boards. We have too many critters that could get in the coops, we build them like fortresses.
I agree with the earlier post, don't leave food out for them! Our feed stays IN the coop, and treats are gone before they hit the ground. If you have a compst pile, enclose it in a garbage can or hardware cloth framework. Our cat doesn't go out due to coyotes, but our three German Shepherds kill mice, rats, and mountain beavers.
Good luck, we hate rats. Hope you can keep them away!