Outline in a outline

Hi!
I have a pdf file with a lot of different detail shaft in it. They also are on different heights and the building varies in height aswell. I want to know how many cubic meters the shafts are. Because the building heights varies alot it takes alot of time if I would specify all the heights by hand.

Is it a way I just could decide a height so I could "stamp" out the shaft and get the m3?

At the moment I extrapolated the pdf and set the same heights around in the pdf. The depth decide the  amount I need to cut but ofcourse it doesn't get the right value if I dont have the exact height around. I need a work around this.