I'm very, very new, in fact, I'm a moron when it comes to camping, campers, etc. I've been camping many times with friends and love it, but never have owned one. My friend has offered me her camper ...
If the floor is soft from a long term roof leak then the freebie may not be such a great gift if the plan is to enjoy the rig for the foreseeable future. First thing I would do is get on the roof and crawl around and see how it looks. Good luck