Fit out is incremental as required, which is a sensible way to manage capital.
I'm not sure what level of fitout has been done in the unused data halls, but I'd expect them to be fairly barren.
I'd expect significant fitout costs as expansion is required. Which should range from new/augmented Electrical Grid connections, High Voltage Switchgear/Transformers, DRUPS, Redundant Low Voltage Switchgear and all associated Cabling. New Chillers/Cooling Equipment. All the catenary systems and wiring to distribute power/comms. Then you have all the racks to purchase and install.
Have a look at some of the ongoing upgrades happening at S1.
http://www.nextdc.com/blog/new-chillers-Sydney
From what I read B2/M2 is only being constructed for an initial 1.5MW & 2MW. M2 will eventually scale out to 25MW. (25MW would easily represent a $10M+ investment for the Utility).
(20min delay)