To export a2D DWG or DXF graphic file:
Manipulate the view of the model so that it appears as you would like it to appear in the exported file.
Select File > Export >2D Graphic. The Export2D Graphic dialog box is displayed (Microsoft Windows).
Enter a file name for the exported file in the 'File' name (Microsoft Windows) or 'Save As' (Mac OS X) field.
Select the DWG or DXF export type from the 'Export type' (Microsoft Windows) or 'Format' (Mac OS X) drop-down list.
(optional) Click on the Options button. The DWG/DXF Hidden Line Options dialog box is displayed.
(optional) Adjust the options in the DWG/DXF Hidden Line Options (Microsoft Windows) or Export Options (Mac OS X) dialog box.
(optional) Click the OK button.
Click the Export button.
by the way this feature is available only in the pro version of Sketchup.