Hi Bob, and welcome to the forum
The DWG importer in SketchUp is unable to see the special objects (like walls and roofs)created by ADT, so you must export them in a format that SU can understand. ADT has a function for this, called Export to AutoCad. The results of this operation depend on your current view in ADT. From a plan view, you get a 2D plan drawing, and from a 3D view (isometric, for instance), you get a 3D model.
When importing the DWG, check your import options (button in the right bottom corner of the Import File dialog box) and check the "Delete coplanar edges" box. That will save you a lot of cleanup work, and the imported model is not so heavily triangulated.
Anssi