I'm from the "No built in ladder for my Class C" crowd. At home I have 12' ladder that works just fine. I do not want anyone having access to my roof from a built in, probably flimsy factory ladder. Just another potential source of leaks.
If you ever have an urgent need to get up on top to check something look around your CG.
Just about every class A and fiver out there has one hanging off their rig somewhere and if you ask nice I seriously doubt they would refuse a request to borrow it. Most camp hosts also have a ladder in their site.
:C