Well if you want to make it out of Legos, you can still use an Arduino as the brain. This link HERE is my video where I have done just that. It can be controlled via Bluetooth, so I can use a computer, tablet, or android phone to control it. Right now I am using a wireless PS2 controller to control it.
Making it out of Legos, is easy. I was going to suggest you use Lego treads, but since you mentioned you wanted it to look impressive, I scraped the idea.
Yeah. Well, the LEGO model is just an example. I would want to do my model, if it will be possible, with aluminium. :)
Wait a minute...Are you telling me that the LEGO Technik can be hacked with Arduino and that they can work together? :astonished: