This is great! Never thought of that. Do you have a way to calculate cut versus fill?
a Set aside (a copy of) the original unrevised mesh. Calculate its volume, using the Element Information palette, an Interactive Schedule or whatever. (Take a note - but it will not change unless there's a landslide or earthquake
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Now, if the bottom foundation slab cuts through the site (mesh) surface, so you have to do both excavation and padding / fill:
b Place the slab (or hidden operator). Cut the required hole / pit using SEO, Subtract with upwards extrusion with the original mesh as target and the slab as operator. (If you want more exact estimates, you might use roofs as operators as well, to cut the hole's sloping sides). Check the remaining volume, subtract that from the original's (with a calculator, not SEO), and you have the cut volume. (edited: The Element Info palette will give you both original and trimmed volume in one go, so actually there's no need for step a)
c Now turn on the layer with the mesh you revised for the house pad. Using SEO, Subtract with upwards extrusion, the original mesh as operator and the revised as target.
The revised mesh will now only consist of the fill volume, check that.
And you have both cut and fill!
It might be easier to buy and use Architerra, if you do this a lot.
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