[ShaBoom]

Originally Posted by vtirocz

The roof skin would provide NO structural support. I think your assertion above is absurd. The thick A to B pillar plus roof bracing is what provides the structure. That roof skin could be removed altogether and would have no impact on torsional and bending stiffness.

With that said, from a cosmetic standpoint, I would be disappointed in what you've described.

See frame here:
Camaro: http://ye-en.chevroletarabia.com/con...ety%20Cage.jpg

Cadillac ATS (Alpha Architecture): http://images.thetruthaboutcars.com/...te-550x366.jpg

Not absurd at all sir. The roof sheet metal being bonded to the underlying structure adds a substantial amount of torsional stiffness to the body structure.
If the underlying structure was all that was required, the roof would not be buckling. This is somewhat similar to stressed skin wing construction in an aircraft where the outer skin is part of the load bearing structure.