What constitutes a suitable location for a beowulf varies wildly, as one might expect given that beowulf designs vary wildly. You might be getting only eight nodes in mid-size towers, or you might be getting 128 nodes in racks. You could be getting eight nodes in a rack or 128 nodes in mid-size towers. You could be building a ``blade'' style compute computer with 32 more nodes inside a single chassis mounted in a rack.
God knows, you could even build a beowulf by buying motherboards with CPU and memory, adding NICs, and hand-mounting them in e.g. a common filing cabinet (fitted with a power supply, some cooling fans, and some spacers). With rack (and case) prices being what they are, I've come dangerously close to building a beowulf exactly this way at home and (as PXE/bootp NICs get ever cheaper) I may yet do it. It would actually be kind of fun...
In addition, you might be building the beowulfish cluster just for yourself, and want it in or near your primary workspace. Or you might be building it for a group of users and need it accessible to the group. Or it might even be a ``public'' facility and need to be accessible to several groups.
Even noise can be a factor. Our cluster room, between the 3-meter-cubed heat exchanger and blower in one end and several hundred CPUs (each with their CPU fan and an associated power supply and case fan all running at the same time) has roughly the noise level of a 747 taking off - on the outside of the plane. Not quite painful, but it's trying. One can hear it through a solid wood door and concrete block walls fifty feet or more down the hall.
Your computer cluster will need a space that meets your own particular constraints of accessibility, noise and security isolation, node design and denstity. Let's start with the simplest issues; how much space will it require?