I agree with the OP, we owned a 2006 Coachmen Cappy an the roof was high except the bedroom which was still high enough to walk around in without banging your head an I'm 5ft 8inches tall ...
Allot of trailers now day do not look like the are slanted but if you look closely you will see that they slant toward the back somewhat for drainage ...
We bought a Kz G384RLT ( https://www.kz-rv.com/products/durango-gold-fifth-wheels/G384RLT.html ) two years ago which has three slides, the door in the main slide not on the side of the trailer which gives us more room ... The kids stated that the trailer inside when opened up is bigger than their first apartment an we have a ton of cabinet space along with higher cabinets ...
Happy Hunting an if buying a unit look for a Post Delivery Inspection (PDI) list to go buy so you are a informed buyer, here is one I made up on the Kz Family Form ( http://kzfamilyforum.com/thread/1903/pdi-list )
Safe travels :)