I just completed installing a Robbins glass window top myself on my 2000 Boxster and wanted to share some of my experience. I purchased mine from Topsonline off of eBay in original A5 canvas for $695. It arrived promptly and came complete with the harness for the window defroster and installation instructions. I also had the original Porsche instructions and Service Bulletin in addition to reading everything I could find about the job on this forum. I have to say that the instructions from Robbins were pretty good and included lots of photos. The only part I struggled with a bit was removing the plastic slide and clamping rail arrangement out of the main bow on each side. In this respect the instructions were vague and the procedure from the Porsche manual was just plain not possible. Once it was apart and I was able to see exactly how it fits together it made the assembly a lot easier. I will say though, that Porsche didn't leave a lot of room to squeeze these parts in and out of place from the main bow.
This was the first time I've ever replaced a top so I took my time working very methodically and slowly. If I had to do another my guess is that it would take me about 8 hours. In my opinion it is well within the capabilities of most DIYers, just requires a lot of patients and attention to detail. The fit is excellent. As good or better then the original with no wrinkles. If anything I'm concerned that it is too tight.
I also played around trying to get the best access to the engine with the top in the service position. Access is best when putting the top in the service position with it opened as little as possible at the front. In this way the window can pass just over the top of the roll bar which helps a lot. I would consider engine access greatly compromised in comparison with the plastic window top, but in the end still sufficient for probably any engine work.
I now understand why Porsche advises that the tension straps (the seat belt like straps on both sides) be replaced together with the top. At first this made no sense to me. Now I understand. Presumably, over time the straps and top stretch naturally in tandem, allowing the tension load to be partially carried by the straps. My new top is so tight that it took quite an effort just to close it. I did not replace the old tension straps and they now hang slack and don't carry any of the tension. I'm a bit concerned that all the tension is now carried solely by the top. The amount of force needed to close it makes me worry that the seams or fabric connection to the window might eventually give out. From what I've read in this forum, it is apparently normal for a new top to be very tight and after a few days it should stretch and require no more then normal force to close. Mine has been in the closed position for 5 days now (albeit parked in the garage) and it is still as tight as ever. I still have to manually force it forward to get the hook to catch and then use a lot of force on the lever to close it. I would be very interested in hearing about any experiences (good or bad) that other members have had with glass top conversions. I've read about some of the problems with the earlier GAHH tops detaching from the window, but assume that has long since been resolved and no longer occurs. Right ??