When I asked R/Art about a sunroof on my E. 6 was told they did not offer them as they had had a lot of problems with leaks. I must say I have never missed having one and to be honest how often do you use them!
To let the sun through the roof?
Personally I have never seen the point of 'em anyway. They leak, increase drag open or closed, decrease shell stiffness and let the sun bleach the interior if you don't have a shade. If you are desperate for a sun roof get a convertible if not open the window!