Making armor requires a whole kit of metal working tools that most people don't have lying around the garage. Here are three good mail-order sources for tools at a discount.
The ideal tools will be a shear like this and a hole punch like this, although you can get by with a saw and a drill. If you can cut, punch, and bend metal, you are well on your way.
This is an extremely cool little cutter at a great price. It works like a can opener! The 16 gauge advertised is a bit optimistic, but for thinner metals it's a breeze.