IMHO -i don't think Windex is the way to go. It may have some of those nasty ingredients that GM says to stay away from.
Cleaning a Removable Roof Panel -
Special care is necessary when cleaning, removing
and/or storing the roof panel.
Flush with water to remove dust and dirt, then dry
the panel.
Clean the panel with GM Glass Cleaner. Leave the
cleaner on the panel for one minute, then wipe the
panel with a soft, lint-free cloth.
Don’t use abrasive cleaning materials.
If water drops are frequently allowed to dry on the roof
panel, impurities in the water will adhere to the top.
These impurities may etch or mar the finish. When the
panel gets wet, you should dry it off.
NOTICE:
Do not use a glass treatment or conditioner
containing ethyl alcohol or ethyl sulfate on the
roof panel. These products may damage
the panel.