CREATE CONTOURS.

Ii is really simple to create a 3D contours in revit. The only important thing is that it have to be a 3d cad data.
Every contour should have elevation. First image is of Autocad plan and second image is in elevation.

Now u just have to import the file to revit and follow the procedure in following images.

Go to Massing & Site Tab>Create From Import>select proper layer>Hit ok and its ready.

Now u can add building pad to toposurface as per your requirements. Basically it is decided as per slope as try to have minimum excavation or as per design inputs.