The National Petascale Computing Facility includes 30,000 square feet of raised floor data center space. Currently the power distribution units are set in place for the Blue Waters supercomputer (shown above), with room for 114 IBM compute nodes that will be placed in between them on the floor. The additional raised floor space will be used to house a 500 Petabyte archival tape storage system as well as network distribution cabinets.
What will Blue Waters look like? In this video from the ISC 10 show, Thom Dunning from NCSA provides a look at one of the nodes that will power the powerful supercomputers. The NCSA segment begins at about 3:45 into the video.
That kind of computing power requires serious power and cooling support, which in turn drives some of the design considerations. A six-foot raised floor separates the server room on the upper floor from the power room on the lower level, and level contains trays for the massive power cables, pipes for the chilled water supply and return, and a two foot deep cable tray (seen in photo below).