Stock roof (for now at least
), and this would be for the outside of the van. It would be cheaper (much!), less work, and less permanent than painting white (although that crossed my mind too)... So somewhat of a temporary/short term solution (that would be cheap) until a pop top is installed.
Reflectix inside the headliner is also on my list (but a pop top may come first, funding dependent). I already have reflectix "screens" on the windows which seems to have helped, but if this would add a secondary "proactive layer" for the roof, then it could even further improve above and beyond reflectix inside the headliner.