what kind of cage do you have? if it's some sort of wire, you need to be covering the wire yes, but not with bedding. use fleece or terrarium liner made for reptiles (i can be more specific if you're interested since it's reuseable and most of the time doesn't get shredded). but it's important to protect their feet from the wires because it can cause something called bumblefoot, which is not good. very painful for your rats. the bedding i would say maybe an inch thick or so? i make sure the entire floor is covered with some extra so they can dig, push it around, do what they want, build nests, burry food, ect. do rat things lol. hope i helped.