As well as the standard Elevation options that can be applied to Point and Polyline shapes, Arcv2CAD gives the option to extrude Polygon shapes to form 3D objects.
Extrude Polygon to Form 3D Object
This option allows polygons to be extruded based on the 'Elevation' value and optionally a 'Base Elevation' value. For example a 2D shapefile of building layouts could be exported as extruded 3D objects representing the buildings. e.g.