For what is is worth, I did an expedition last year and one vehicle in our group had a roof tent. I was not all that impressed. Sure they look great but once set up you are basically stuck. We had an Oz tent which goes up in minutes and allows you to still use your vehicle. We had a couple of days where we went back to the same camp site and we could leave all our camp stuff set up and go off for a day in the hills. Another thing was, the ladder broke on the roof tent (luckily, no one was hurt) and it left the tent pretty useless.
They are also bloody expensive for what they are. The Oz tant is also bloody expensive but we already had that.
aman