My Merc SL spent Quite a bit of time under a Halfords, breathable outdoor cover and survived very well. £70 iirc.
To avoid any scratches and because of the large size, I used to take it off by starting at the front.
Unhook the elasticated front from under the bumper and bring it up and over on itself to the mid point of the pan roof so it was folded outside to outside.
Do the same with the back and fold it back on itself until it met the front edge, on the pan roof.
Go to the folded edges of front and back and fold those to the roof, mid point so they are inside to inside.
Now's the only time any of the cover slides over the car.
Fold the front over onto the folded back, again, inside to inside while sliding the whole lot forward to a central balanced point.
You now have the whole cover in a ~1M width but hanging down at each side.
Starting on one side, raise and single fold to the mid point of the roof.
Go to the other side of the car and raise and fold that to meet at the mid point.
You can then, whilst carefully drawing the whole thing towards you double that side on to the top of the first side.
You now have a neatly folded cover with outside to outside and inside to inside.
When you want to re-cover the car, just place the folded cover on the glass roof and unfold in the reverse sequence.
Well it worked for me and my O.C.D.

for 5 years without any scratches.