Things that come to mind are:
Enough power for all the desktops. I’d guess about 700w per PC (if CRT monitors don’t forget to include them)
Building AC for users and data center
If you’ll have TV’s, vending machines, microwaves, etc in the break room they will need power as well.
The cleaning crew will also need power for thier machines at night. Make sure that there are enough power outlets in the walls for the vacuums, etc.
Any network switches which will be in IDFs not the data center