What parameters affect the amount of btu required to cool a single room
Some key parameters:


Size
Peak Outdoor Temperature (i.e., needs to be sized based on the hottest days)
Insulation
Windows - size of windows and also quality (double or triple pane will do a LOT better at keeping cold in/heat out than single pane)
Frequency of opening of doors to the outside
Air Leakage - cracks, holes, etc.
Internal loads - how many people? computers or other equipment? A room full of servers generates a lot of heat.