You can import 3D DWG's into Revit, but they will not convert the solid geometry to Revit massing or building components directly. You need to inport the AutoCAD 3D into a create mass in the massing editor and then you can face the mass with Floors, Roofs, Walls and Curtain Systems to start the development of your model.
Mel Persin, AIA
AEC technology Consultant
Technology to Visualize and Realize Solutions
Modeling the Future/Drafting the Present/Building the Past