If you are going to have servers, backups and other items that are both mission critical and environmentally sensitive then you need space that is air condition

If you are going to have servers, backups and other items that are both mission critical and environmentally sensitive then you need space that is air conditioned, expandable, properly sized for power and lockable. Unless you are both a licensed electrician and a trained HVAC engineer I guarantee you that whatever assumptions you have about servers and their power loads, heat signatures and space requirements are wrong. Unless you are planning on hiring full time IT staff, you probably don't want to build your own datacenter. If you think you are going to get much much bigger (server wise) then you might want to look into buying a small (but expandable) amount of rackspace in a datacenter. This will place all server infrastructure issues at somebody elses feet. If you think that you'll buy three or four servers and not expand beyond that for the life of the business, it's probably a good idea to simply modify a large closet (> 150 sf) for AC, UPS, power, etc... But if you think you are ever going to have more servers then that you need to think about expansion now. If the servers are critical to your business then you'll thank me later...