TARDIS's aren't built, they're grown. And if you watch "Torchwood", there's a growing TARDIS on Captain Jack's desk.
Strictly speaking, TARDISes are grown from a more than just TARDIS coral. The coral provides a link to N-space for Block Transfer created matter to be grafted to. The coral forms a central portion of the TARDIS. The TARDIS coral itself, however, does not directly become a TARDIS. It takes other processes, equipment, and "morphologically unstable organic matter", and mass amounts of equations, to fully build the TARDIS, most of it being non-atomic matter (matter made up of something other than atoms) created by Block-Transfer Mathematics.