I was working with room volumes today and in creating my room schedule I noticed the words 'Not Computed' in the volume cell. I hadn't seen this message before, so I did a quick search and realised I had not turned on volume calculations.
By default Revit has this turned off for performance reasons. It's an easy enough fix, simply go to the 'Area & Volume' Computations dialog. It can be found on the 'Architecture' Ribbon on the 'Room & Area' Panel. Click the drop down menu and select 'Area & Volume Computations'.
Now switch on Volume calculations by clicking the radio button.
Now the volume displays in the schedule.