Other than Warren Buffet most billionaires live in massive mansions that spread across acres of land. Check out this link to msnbc.com.  Take a look at Home's of the World's Billionaires including Michael Dell and Bill Gates who both have homes exceeding 33,000 sqft. I don't even know what I would do with that much space...I'd have a huge garage and indoor basketball court...other than that how big do you need your family room to be?