Coke cans will work well, I think. Thin styrene sheet will work and so will something like a cut up aluminum pie tin (the disposable kind). If you want a bunch to work with, pick up a disposable aluminum turkey roasting tin. There's enough metal there to build a whole battalion of Tigers.
My LHS carries brass and aluminum metal pieces including tube (for barrels), L and I beams (great for Dioramas), and flat pieces. Pieces of flat brass or aluminum like these would work very well.
Enjoy your modeling...