You really want to build a robot, but are really concerned that some of your upfront design decisions will lead you down the wrong path, or that you will have to trash expensive sheet metal and fabricated parts after weeks or months of hard work. It's a common concern for both robotics hobbysts and professional robot designers alike.
Why not prototype your design, and prove your concepts, as quickly as possible, using cheap, readily available materials that are easy to fabricate? Common, everyday items like cardboard, sheets of plastic, and similar materials. After you develop a confidence level that the design is really going to fly, then you can go back and invest the time and money to fabricate the robot parts out of sturdier stuff.
Cardboard? Did I say cardboard?
Yes - absolutely. That's exactly the approach used and documented in wonderful detail in the Wireless robotics: Fast robot prototyping article published by Erik Zoltan on the IBM developerWorks website. The article also includes links to other useful articles covering how to drive a wireless robot and a recipe for success in wireless robotics.