scheduling site components

[mob]

I have been asked to create a hardscape schedule for our template (we are residential architecture) and I'm having trouble w/ getting area information. If I schedule by object, I can't get an area calculation, if I schedule by material, I get the total surface area. ex. an asphalt driveway area calc includes not only the top area, which is desirable, but it calculates the sides and the underside as well!

any suggestions on how this can be done?