The way I lay out the equipment room is to use X and Y coordinate system based on 2 square foot intervals. Using a four character identifier scheme consisting of two letters and two numbers. The letter identifier precedes the number identifier. Imagine your room with an X and Y axis, the letter identifiers should be assigned to the longest axis and the number identifiers assigned to the shorter axis. This permits the the highest number 4 character identifier combinations. Skip the letters I and O because they can be confused with the numerical identifiers. You should start your identifier assignments at a load bearing or permanent corner of the room. In the future, if the room is ever expanded, your identifier system will not have to be renumbered because you started at a permanent wall.
As far as labeling the wall, I recommend 8" tall letters about 9 feet above the finished floor. You don't need to label every 2 foot interval on the wall, you can space the labels out every 8 or 10 feet.
To assign a cabinet or rack to a floor grid coordinate that touches more than one floor tile (or coordinate), you need to standardize on a rule for determining which floor tile or coordinate will be assigned to the cabinet or rack. The way I do it is using the front left corner of the cabinet or rack that touches the floor tile or grid determines the cabinet identifier. For example, a 30 inch wide cabinet front rests on floor grid AA17 and AA18. The front left corner touches AA17 so the cabinet will be labeled and identified as AA17. In the case of racks that have vertical cable managers on the left hand side, I still use the front left portion of the rack as the point of reference instead of the vertical manager (not all racks have vertical cable managers on the left hand side).
If you are in a multi story building with equipment rooms on each floor, you can add a floor identifier in front of the letter identifier. Using AA17 example above, if that cabinet was located on the 20th floor, the identifier would be 20AA17. The floor identifier is optional. This is handy when you want to identify backbone cabling termination locations that runs from the equipment room to the telecom rooms located on different floors. This can be used for everything in the equipment room, CRAC units, shutoff valves, splice box locations, sleeves, etc.
