How do I build a charging station for 12 iPads?
Datamation offers a multi-charge/sync setup now, and apparently Parat solutions has one in the works.

If you're looking to build your own, the Datamation unit uses a Cambrionix C3 board with 16 USB ports for charging and syncing. You could integrate it into your own solution. 

You could also just get a 12+ port USB charger, however charging and syncing may take significantly longer this way. The Datamation site has some charge/sync time tech specs that support this.