You can't run it monthly, because that won't show the peak. That would just show you the monthly utilization. It does depend on how they want to view this. Do you need a breakdown per building, or is it really an over-all view of the total utilization? 

And I'm not sure if I get your statement about the challenge: if you have 1000 desks over 5 buildings, it doesn't matter if one building is on a 100% utilization and the others at 0%. The total will still be 20%. Unless it's per building, but then there also isn't a challenge. 

What you could do is collect the complete data with breakdowns per building, or collect it per building and use formula indicators to show the total (that would help with the challenge, since you are adding the building utilization to get an average).