Very good one.
But I'd like to ask. If the example is a glass building, all the surface are glass. How would it be? Do we need more cube map?
I wouldn't make a separate cube map for say each side of the building,.. because it would use quite a lot of memory,..
The default "cube map" or environmental map,.. its a general representation,.. for trees, hills, and without buildings. So for instance, with say a downtown area where a lot of buildings around other buildings,.. the default cube map wouldn't be the best fit.
What I would do, would create a "cube map" for each general region,.. the default would be best for the rural areas,. another for a city or downtown area,.. and so forth...