I suppose another option would be to bracket your pictures, meaning take several pictures at different exposure levels and merge them into a tone-mapped picture. I don't want to use the word HDR, but it is possible to take a HDR program like Photomatix and make tasteful HDRs that look natural.
Another possibility to consider is stitching... taking multiple pictures and interconnect them together to make one larger one. AutoPano is the most powerful software out there that handles panoramas with ease.
In the end, a lot is going to depend on:
- your equipment (specifically quality of the lenses available to you)
- the size of the object(s) you want to get into the frame
The bigger the picture, the trickier things will get, as the candles will get smaller and smaller until they are nothing much more than tiny points of light almost that are individually indistinguishable, or if done correctly, could come out looking like one mass of light, if arranged to form a word or design.
Without really knowing the specifics of the area, what the goals are and the is available to you, all we are doing is effectively shooting in the dark (lol) with guesses.
You mention a roof or cherry picker as a location to shoot from... a flat roof would be better, because if you wished to fuse multiple layers, unwanted movement becomes a strong issue in a cherry picker whereas a roof is not something I expect would shift around from picture to picture over time if your camera was placed on a good tripod.
Think safety above all. Even falling from a 9-10 foot height is enough to cause some serious damage to your equipment and (more importantly), your body.
As far as settings, I do know that best results will be met if you understand how and what to meter against and use full manual mode. Once set, it will not change the exposure from frame to frame and this could be likely the most important factor in the end.
