first, you need to get bottle caps,clean them ,take out the rubber thats inside of it.

now take the hammer and hammer the bottlecap flat, to get it extremely flat you´ll need to turn the cap a little. you may want to put some cloth over the cap to protect the varnish on top of it.

WATCH YOUR FINGERS

you should have a flat round piece of metal.
if there are messages on de sides of the cap youre cap is done(i did so with the aloha-cap) but you can also make the metal-plates smaller by cutting them ,you can even cut them into form with a wire-cutter.

all you need to do now is, to glue the bottlecaps to your magnets.i used old magnets from ugly ones i didnt like anymore, but i think you can buy magnets in craftstores and building centers. i used hot-glue but superglue might do well.
and you re done :)