Yes, bare wire cage floors are safe for Roof Rats. It’s OK if you don’t cover them. Your rats will not suffer any discomfort or develop and foot problems.
You can cover you floors if you wish. However, be aware that Roof Rats chew on everything, and will attempt to shred any material that is soft enough to use for their own nests. They may also attempt to hide underneath the floor covers, which is unsafe as it will put additional pressure on their feet and bodies, may make it harder for them to breath, and prevent them from interacting with you or their cage mates.
For these reasons, we do not recommend that you cover your floors. If you do, we recommend that you use a metal plate which is completely welded on all sides so that they cannot go underneath it and there are no sharp edges that they can reach with their paws or nose. Any other material, such as cardboard, felt or plastic, may potentially cause more harm than good.
Many people believe that Norway rats will develop foot problems if they live in a cage with wire floors. For this reason, if you post any photos or videos of Roof Rats in a cage with visible wire floors, you will attract negative comments and helpful advice about what you are doing wrong.
Many well intentioned and experienced owners of Norway rats are simply unaware of the differences between Roof Rats and Norway Rats. They reason that because metal wire is hard and applies pressure to a relatively small area, it must be equally hard on the feet of all species. But, not all feet are made the same. Roof Rat feet are adapted for climbing hard, rough surfaces, and hard tough, thick pads that Norway rat feet lack. Their feet and legs are much larger and more muscular for the rat’s size, and more nimble and flexible. They can climb around upside down on a wire cage almost as easily as walking horizontally. In fact, they do it for enjoyment. The wire doesn’t appear to bother them.
While they are resting, they will normally be in their hammocks. If they do chose to rest on a wire floor, they naturally distribute their weight such that there are no uncomfortable pressure points, just as they would if they were in a nest made of twigs in a treetop.
Finally, because they evolved for a life climbing and jumping nimbly in trees, Roof Rats are longer and more muscular and slender for their size than Norway rats. They walk lightly and silently on their feet, as you would expect for a rat that is able to quitely navigate twigs and leaves a hundred feet above the ground while avoiding the attention of predatory birds. Therefore, they do not put the same pressures on their feet that Norway rats do.
None of this will probably be enough to convince experts you encounter online that what they know is true about wire floors for rats isn’t true for your Roof Rats. That’s just the nature of the Internet. If you do post any videos on Reddit with visible wire floors, especially, be prepared to be downvoted and lectured by some people. My advice is to ignore it: your concern is making your pets happy, not some anonymous strangers!
But, if you can, try to take photos and videos where the cage floors are not visible!