It is very hard to achieve full coverage across a site with grading objects. A much better workflow I would suggest is to start by running a feature line around the outer perimeter of your site, lay this feature over existing ground and then use it to build the outer boundary of a proposed surface. This way, you start with a sort of flat sheet proposed surface, you then paste your corridor surfaces for roading, lots etc onto that surface to add definition. Think of it as vacuum forming, the hot plastic sheet is your starting surface and your corridors are the wooden model that add shape. The reason I recommend this workflow is you don’t need to grade every inch of your site, just the important stuff like your road corridor and building pads, the rest of the surface will fill the gaps and do the grading for you.
Mike Kingdon
Civil 3D Zealot
