The gift cards are the perfect size and shape for it. And you can make the magnet several diff ways. For example, for the USA magnet, I painted the card with 3 coats of white acryclic paint and then painted the design. Whereas, in the India magnet, I used pieces of craft foam to make the design. You can also use paper cutouts and cover with a layer of mod podge.
Have fun with these and don't forget to send me pictures of your magnets.