TRau gave some good tips. Some other things to take note of:

• Don't forget about a backup plan! There are times when power fails and the backup power grid also fails (the Northeast grid blackout a few years back is an exaggerated example). So, be sure to have a contract with a diesel company or gas station to run diesel/gas powered backup generators capable of running your servers at full or limited capacity.
• When placing the servers, it is better to stack than to place back-to-back or even front-to-back. Basically what I mean by this is keep the fact that servers generate heat in the back of your mind at all time. You don't want the server fans working 100% of the time when they don't have to. So, try to avoid this by choosing good server placement.

There's probably some other stuff that I'm forgetting. So, you may see some addition bullets pop up here later in the week.