We get this all the time. What we have done is list the minimum equipment required in a closet (HVAC, conduits, switches, PDU's, patch panels, everything) and then lay it out in Visio. Make sure to account for things like ladder racks, 36" clearance (or whatever code is in your area). Once you do all that you will know the minimum size room you need. Then lay that room onto the overall floor plan. Then using Leo's number you'll know how many closets per floor you need. I get that they will complain, but there is a limitation of cable distance and there is nothing we can do about that. Give them the data and let them figure it out. It's either that or they don't get a functional network.
FYI: Here's a couple of things to watch out for/suggest:
- Get a 36" door
-Make sure they account for water dispersion from the A/C unit
-Be sure to give them BTU's and power requirements
-Overhead lighting (should be two rows, one on either side of the rack)