My suggestion is to use the Grading tools to create the grades. For example, I am doing the same thing on a commercial project, grading sever building perimiters to an absolute elevation. However, once I have the grading objects created, I explode them and add to surface as breaklines. Then, I have a very dynamic enviroment to raise our lower building pads by leveraging the fairly reliable surface object. I am convinced you can do very complex grading with Civil 3D but currently there are some grading tools you need to avoid.