So, here are some note needed to know about how quantities are calculated.

NET VOLUME AND GROSS VOLUME
The difference between gross volume and net volume is that the gross volume is calculated
without the related IFC opening.
So, if an object is created lets say with a hole but without defining the opening, the hole is counted into net volume (so get volume and net volume are the same).
This is in order to follow the native IFC approach.

WALLS AND BEAM LENGTH, HEIGHT, WIDTH AND LATERAL AREA
These dimensions are calculated with the convention that the object can have main axis along x or z. 
The same with lateral area.

SLAB THICKNESS
The slab thickness is defined as Width, following the IFC definition
Also, note that these dimensions are calculated only if the slab is prismatic.




