Use OBJ Export to export your Revit model to an OBJ file.
- Open a 3D view.
Note: The exported geometry will be based on the current view. Geometry exported will reflect the visibility and graphics settings of the current view.
- Click the File tab
Export
CAD Formats 
OBJ.
- In the OBJ Export dialog , specify your OBJ file settings.
- Click Save to create the OBJ file or click Cancel to close OBJ Export dialog.