The CADspan Plugin for Google SketchUp allows generation of solid, 3D printable STL files directly from a Google SketchUp model.
The plugin provides several tools to ease the process of preparing a model for 3D printing:
-Resurfacer: Shrinkwrap a model into one continuous, solid mesh
-3D Print Visualization Style: A visual style that highlights problem areas in a model
-Layerize tool: Easily move all geometry within components and groups to a layer
-Smooth/Unsmooth: Toggle smoothing on a model's rounded geometry
-Free Version for personal use and small applications