Used Fleetwood or Jayco

I don't know how long they last. If the unit was stored under a cover, the roof could easily last decades. Mine, which lives outside fulltime, is 13 years old and is starting to look pretty rough. I plan on coating it this year with some kind of liquid rubber or related product. I think that could be done to pretty much any roof, and would expect to do it to anything older than 10 years, which is the typical material warranty. If the rest of the trailer is in good condition and suits your needs/desires, don't let an old roof stop you (unless you can't or don't want to perform that maintenance). RVs, especially these older box on frame trailers have routine maintenance requirements that you really can't put off. The roof and exterior walls are full of potential leak locations that need to be dealt with before they inevitably leak.