Making your home rat-proof is next to impossible, but you can take steps to keep the pests at bay. They can chew through most building materials, including wood, plastic, weak concrete such as cinder blocks, aluminum sheeting, and even some glass. Changing your flooring to a rat-resistant material can discourage the rodents from making your home their home.
Rats can gnaw their way through weak concrete, but solid concrete surfaces are a different story. If your home already is on a solid concrete foundation, it's unlikely the rats can enter through your flooring, even if you have carpet or hardwood on top of the concrete. For homes on crawl spaces or basements, adding solid concrete flooring to the upper floors can keep rats from gnawing through, but have a professional home engineer check out your house to ensure it can withstand the extra weight. Finish the concrete with acid washing or lay regular flooring on top to hide it.
Rats can't eat rocks, so stone flooring can help keep them from getting in through the floor. This isn't necessarily true of ceramic tile, which can sometimes be weak enough to let the pests through. The problem with stone flooring is that weak points often exist throughout the room; it's normally installed in a pattern with grout between the stones, and the grout provides an easy entry point for rats. Small grout lines aren't wide enough for rats to squeeze through, but they only need a hole about 1 inch in diameter; they might find these in the corners of your floor or along the grout lines of any special designs in the stonework.
Metal isn't exactly a traditional residential flooring, but several options can help strengthen your floors. These are typically laid with the ends butted next to each other with no grout in between, similar to hardwoods. Some metal tiles have the appearance of hardwood as well, while others provide more of an industrial look. The flooring should be made of a tough metal such as steel to deter the rats; soft metals such as aluminum are no match for a rat's teeth.
When you've chosen a secure flooring product, that doesn't mean your rat problems are over. Rats can dodge the flooring and chew through wooden baseboards or your walls, especially around areas where holes already exist, such as around pipes and wires. When you notice existing holes, even tiny ones, wad up some steel wool and press it tightly into the hole to discourage the rats from making the holes bigger.