That is the beauty about class C's. There are so many concepts with their design. Some sit taller for improved under-the-floor storage, some sit lower to reduce the house/cab step for better use of the passenger swivel seat, and have lower steps or fewer steps to get in from the outside entry door. Then there is the varying interior ceiling height with consideration to the front cab-over bed and whether the roof a/c is ducted.
Something to keep in-mind is that the higher they are, the higher the center of gravity is, the more compromised the handling will be, especially on windy days with a huge side wall getting blasted by gusty cross winds.
Some E-Series class C's can be 1-1/2 feet (18") taller than others. Our rig is small by most E-series standards with only 9'-10" to the tippy-top of the a/c unit outside. It's not for the over 6 foot person (with shoes on) for you would be dodging everything attached to the interior ceiling like light fixtures and ductless a/c unit. But if you are 6' or less, it's a sweet size.