Dedicated computer rooms don't have to be large to be effective. When we moved, the new computer room was half of the size that we occupied in the original building. The difference is that we moved non-essential items out of the computer room, leaving it to just operations. The new design is much more efficient (see figure).
Figure 1 An efficient computer room layout, incorporating only essential operations.
To make the best use of our floor space, for example, we implemented racks. Prior to the move, we had begun using racks, but still had several servers sitting on countertops. When the opportunity to move presented itself, and the timing was right to upgrade servers, we switched our form factor from tower to rack mount. Rack-mount servers are not as tall as tower servers and can therefore be stacked in rack cabinets for higher density (more servers per square foot). Rack-mount cabinets are about 2 feet wide, 3 feet deep, and 7 feet tall. You can get more than a dozen servers in a single rack.
You may have heard the term 19" rack mount. Nineteen inches is the inside dimension for the width of the equipment that mounts into the cabinet. Another rack-mount term you should know is rack unit (or just U). One U is 1.75 inches in height. Servers and other rack-mounted network equipment are listed in number of U's. For example, one of the new servers we bought is 2U or 3.5 inches tallthat's not tall at all, and very powerful, as it contains dual processors, four hard drives, and still has a floppy disk and CD drive. To get all of that power into such a small space, rack-mount servers are very deep; about 2.5 feet is what we have.