Calculate Parking Stalls based on area from zones

[Scott Bulmer]

Greetings,
I am unable to figure out how to create a parking calculation schedule based on measured areas and use categories input into zones. I tried adding a 'Use' property which one could select the ratio of stalls to area, but I was unable to make the calculation. It would be great to sum up the areas per use and then multiply against the parking ratio to return an answer of required stalls. Any thoughts are welcome. Thanks!