I have repaired many cars over the last year or so, that where hailstone damaged in storms around Leicester, particularly the Hinckley area.
All the cars that I have repaired, needed new roof panels, though some were lucky, and I know got away with a Dent repair specialist doing "What they could" to thousands of lesser damaged cars!
The roof panel on a Mk6, has 2 swage lines that run from the windscreen, to the tailgate, either side of the car, and I'm sure that the Mk7 will be constructed in exactly the same way, as its only a face lift of the Mk6
These "Swage lines" are in fact precision joints, cleverly disguised, that are spot welded, and/or bonded to the "Cant rail" underneath...
To change a roof panel, you would need to remove the front windscreen, and the tailgate, and pretty much all of the interior, including the delicate headlining. Doors should also be removed to avoid grinding and spark damage to the trim, and glass... sparks hitting glass will permanently damage the glass, and will need replacing, this is very common in body shops, and is generally overlooked!
The steel roof panel would then need to be cut away from shell of the car, this would the reveal the remnants of the roof, that are spot welded to the Cant Rail, spot welds (Probably over a hundred of them) would then need manually drilling, very carefully to avoid drilling going through both panels... bonding sealer would also have to be cut manually from the car, then the fitting edges would be ground to bare metal, on the shell, and the new roof panel, so that a good electrical contact is made prior to spot welding... at this point your car has lost its anti corrosion integrity, that VW carefully builds into its cars in the dipping process!... you get the picture
If the roof needs replacing, then its a fair assumption that the bonnet would also need replacing, and the wings repairing etc etc etc... expect your new Golf to be fully repainted!
I would also question the turnaround times for repairs, this may be close to the waiting time of a new build...
Knowing what I know, would I want a Hail damaged car at any price, one thats been stripped out, cut apart, and fully painted. Answer, not on your life!
These cars should be repaired by VW, and then absorbed into the market through the likes of Hire car places etc
Thom