If I have a polysurface with a non planar plane. I am projecting shape on it, that would represent constructed lot. How can I remove (boolean difference) the lot shape from the overall land shape ? When I extrude a non planar form, it cannot be cap as a closed polysurface so I cannot remove it from the main object. I am able to achieve what I want but I have to split the shape, extrude the edge and then move the top to the bottom. Quite long when you have a lot of shapes.
When all the object are planar, this is so much easier.