Why can't I import DWG/DXF files?
SketchUp Pro supports the import and export of DWG/DXF files. Up until version 7, SketchUp Free supported the import of DWG/DXF. But with the maintenance release of SketchUp 7.1 Free, supported was removed in exchange for pushing for greater support of the 3D open-source format COLLADA for the future. To ease the transition away from legacy data formats, Google created a free plugin to import DWG/DXF into SU Free 7.1.
Some lively forums threads
Note: Students qualify for a student license of SketchUp Pro, which includes the DWG/DXF importer and exporter.
Third-party Plugins
Using third-party importer/exporters have been possible since SketchUp included the Ruby API in version 4. Third-party importers/exporters may continue to offer the desired support for the still popular DWG/DXF formats.
DXF_In Importer (alpha) by honoluludesktop.
LTPlus AI SketchUp exporter to DXF/SLT from ArchitektenInitiative (German/English)
MeshLab Open source converter. Imports/exports COLLADA and several other 3D formats, including DXF. - Windows, Mac, Linux
skp_to_dxf Export your Sketchup model as a DXF or STL triangular mesh or as DXF lines.
FYI CAD, DXF, DWG Viewer for Drive now offers a DXF online viewer.