raised flooring is a major fire hazard that a good dc will not allow. it also typically creates a cabling mess when somone decides to cable under the floor which eventually leads to an obstructed cabling space.

raised floor is from the old days when large main frames were designed with a hole in the bottom of htem to sit on a hole in the floor to recived their cooling from the plenum space. this is how it was done - unless of course you had a fancy water cooled mainframe like the company I used to work at had.

any way - in the hard core telco centers designed to run at 100% uptime with no hazards you will not find a shred of raised floor.