You can export an Obj file from SketchUp, then import that into AutoCAD 2012/2013/2014 with a Obj importer for AutoCAD from http://www.CodeDog.com.au or in the Autodesk apps store.

Then if AutoCAD cannot convert the object to a Solid use "Polyhedral Mesh to Solid" to convert it to a solid. "Polyhedral Mesh to Solid" is also from CodeDog. This should give you proper solids not blocks.