We shopped for 11 months and looked at several coaches and talked to other campers. We decided we wanted a diesel pusher either a Newmar or Tiffin. We ended up with a Newmar Dutch Star. Our coach is now 20 years old. Nothing Newmar has failed. We replaced, radiator and all hoses, tires, batteries, carpet and refrigerator in the past three years. We are completely satisfied with the coach. I don't know what material the roof is but it seems to be in very good condition.
The roof material should not be a decision factor. Floor plan, chassis type and quality should be.