Just out of curiosity I used 2004 estimates of the 243,000,000 million registered vehicles in the US and average parking space measurements of 8' x 20' feet (160 sq ft) to see how big a parking lot we would have to build to park all the cars in one place. It would take approximately 1395 square miles to park all of America's cars. This is more space than the 1045 square miles available in Rhode Island.
It looks like we'll have to build it in Delaware which currently has enough room with 1955 square miles.