Id say rats get into the loft via wall cavity's from under the ground floor. Especially floors that arnt solid and have a cavity or low cellar. I've seen rats literally dig under the foundations of houses to get in then use the wall cavity as a motorway around the house. Holes in the roof more likely to cause water ingress. I'd prefer to use traps, at least you get the body rather than rotting in your house from poison. I've had rats in my garden for years, shoot and trap them constantly. Once you are on a sent trail very hard to stop, good luck