mine are from old license plates so they have holes. But without the holes would be able to fill them full of water and they wouldn't leak!
I've entered this project in the REUSE contest, Check out the entries and vote on one you like! :D
Step 1: Layout.
Step 2: Cutting.
Step 3: Pre-Bending.
Step 4: Folding. EXTREMELY IMAGE HEAVY!
folding is a process that should be taken slow, hopefully I've provided sufficient photos to walk you through it. start close to a corner and fold towards you if using a vise. help the crease fold outward with a screwdriver and pliers. when you move to the next side stay close to your best looking corner and pinch the corner crease while folding towards you. repeat on all sides. when each crease forms a triangular "ear" you're ready for the next side. put a block in your vise (wood works for soft metals) and fold the ears over making sure they lie straight. repeat all 4 sides. last step Is the edge fold, necessary to lock the ears down and strengthen the whole container. line your vise jaws up and bend CAREFULLY!!! at this point you might tear your corner seam. put your block back in the vise and hammer flat. YOU'RE DONE!!