Here is a model of one of our new robots were building in order to get new team members ready for build season. We are also testing a drive system using this robot as well. I did not go into detail because I didn't think it was really necessary. The way I see it is that sketch-up is good to build off of since you can make models very fast and is really easy to learn and Autodesk or Solidworks is when you want to show off your design. This robot will also have a ping pong cannon built on it.
http://sketchup.google.com/
http://sketchup.google.com/3dwarehouse/details?mid=16ff954c65cb2e99dec8e8e3324cefee&prevs tart=0