From SketchUp free to Unity3D

While there are many ways to go from SketchUp to Unity3D Game engine, having the free version poses serious limits.

• In the Pro version, FBX and Collada export are intergrated and work fine. However, the free version has problems. While there is Collada export in the Free version, Unity3D fails to properly import the geometry.
• One approach is to use conversion software. The Open Source Blender is known to be able to import DAE files from SketchUp and export them into an FBX file that Unity3D understands.
• Another approach is with the LightUp plugin for SketchUp. This is not free, but is a good approach to do shadow and light baking and has an integrated FBX exporter that works fine in Unity3D.

But you can also extend SketchUp with ruby scripts.

On http://forums.sketchucation.com/viewtopic.php?f=323&t=33448 you can download an OBJ exporter script (the old Alias Wavefront format) which Unity3D understands. It is best to export into a separate folder, as depending on how you textured your model, multiple materials could be generated.