[MrForbes]

As far as I know, the rules do not specify what machining or forming techniques you can use. The rules ARE specific about what materials you can use. And there was a discussion about what constitutes "sheet" aluminum, vs. plate aluminum. My guess is that if it's less than 1/4" thick then it's probably allowable as "sheet", but you'd definitely want to ask on the Q&A to be sure.

I'd be looking into learning about how to design and build thin sheet metal structures, if I were working on that part of the project. Look at some past big robots built by teams such as 148 and 217 among others for inspiration. And think very thin sheet metal, as the minibot need not be very big or strong, and in fact probably wants to be as light as possible. In general, milling a huge chunk of aluminum is NOT the most efficient way to build something as light as possible. Also investigate how aircraft are built. Or old Airstream travel trailers. Or an Avion truck camper (which I'm in the middle of restoring right now!)