We have a 2019 Lance 2375. The exterior portion of the roof is constructed of a one piece PVC material and a type of foam insulation. We have been in a number of rain storms this spring and I don't really think the roof is any louder than our previous Class C. We also have the slide out awning so I do not notice any noise in the slide area.
We have one 170w solar panel, and with the 15k a/c, two fantastic fans, antenna, and vents on the roof there's not a lot of empty space.
As others have stated, this is purely subjective as we like the sound of the rain.
Maybe you can go to a dealer and sit in one during the rain.