While I said roughly 4' x 4', the hole I would cut is 43" by 43",
centered side to side and front to back within the 2 main arches. This
puts the side cuts in the flat spots of the middle roof rib. My guess is
  that VW put those flat spots there for just this purpose. This
facilitates a simple finish trim after a hole is cut. You need some flat
edge all the way around the new opening.

It is tempting for people to cut the hole a little small out of caution
but this is a problem on the front edge since if you leave too much of a
lip it blocks your hands from releasing the poptop latch comfortably.
Leave a couple extra inches of the headliner to fold over the new edge,
so cut it more like 40" x 40" and cut any excess after the finishing is
worked out.

Mark

mark drillock wrote:
> I cut the hole and installed my first poptop 15 years ago to make my
> Baja Syncro Camper. It has been offroad many many times, heavily loaded.
>
> As long as the roof arches are left alone, the roughly 4' x 4' hole cut
> over the standing area is not a problem, in my experience. I have put
> 150k miles on that Syncro since. I still have it and I have done the
> same to a few others since that one.
>
> ...............