One of the major contributors to heat gain in buildings is the roof. One-sixth of the electricty generated in this country goes toward cooling interior spaces. That translates into more than $40 billion annualy.
Reflective roof technologies, commonly called cool roofs, are increasingly being used by commercial applications. A cool roof can lower cooling costs by about 40%, per a study by the Heat Island Group of Lawrence Berkeley National Laboratory.
The full article can be found here at the eco-structure magazine website.