i havent worked with google sketch up, but ive heard from friends who have used it say its pretty good. i even heard it from my architectural design professor.
i remember for a while, Autodesk was offering free downloads of their programs, not the full version mind you, but enough to get it going to learn how to use it. it was basically to learn, rather than use it for a profit, because of unemployment on the rise, and they wanted to help people get informed and employed. i dont know if they still offer that. but like i said, its not supposed to be used to gain money in any way from.