Planning a Small Server Room

An anonymous reader writes: "Our company is planning to build a small server room. Initial requirements are for two or three enclosed server cabinets in which various servers and network gear will be installed. The cabinets are planned to hold between 15 to 20 servers of various types and sizes, switches, routers, four dial-in modems for after hours use by staff who do not have ISPs and a KVM switch. We would expect for a small desk as a work area, a book case, storage for some spare parts as well as server documentation and records. We know that we need some power protection in the way of a UPS and a generator. We also expect that this room will get quite warm in the summer months so it will need more air conditioning than the rest of the office. What should we expect for power and cooling needs? Are there any 'rules of thumb' when it comes to building a server room. Good suggestions and help would be appreciated."