A faraday cage is simply a complete covering around the item you want protected. It can be as simple as dropping your item in a cardboard box, then covering the box in aluminum foil. A tin box or metal ammo can would work well. Actually on spacecraft that I worked on we did not even use full metal like Al foil, we used bronze screen, a bit closer mesh than used on doors, but not much different.

I would not trust our oven as a cage, it has a nice window on the front that is glass, good for food, bad as a faraday cage.

Greg