You can delete a selection of AREAL3D-buildings from the toolbar or the context menu.
By this also hidden faces (for terrain modification) are deleted.
If you delete a building via sketchup functions, AREAL3D will in most cases delete the hidden faces, too, and try to restore the terrain.
It can be usefull to clean-up the saved-mesh-layer from time to time (context >> clean up).
Here all hidden faces indexed to deleted buildings will be removed.