The building energy data book is a great general source of information
of all type on US buildings. It draws on several data sources to present
as complete a set of information as possible. (Look at the links to
charts on the left side of the screen for some big picture data.)
http://buildingsdatabook.eren.doe.gov/?id=view_book&c=1
The Commercial Building Energy Consumption Survey (CBECS), which is
conducted every 4 years provides much of the raw data behind the databook.
http://www.eia.doe.gov/emeu/cbecs/contents.html
sam