I'd rather you learnt using Blender, Zloff. With a bit of SketchUp experience it's not that hard to pick up on Blender. But anyway, you can always export it as a .kmz and then get the .dae collada file from there. However, the model is likely to be messy, meaning you may get lots of strange empty meshes that you won't be able to get rid of, no matter how hard you try.