You only need 3 things:
-Scrabble tiles (ebay $5-$15)
-Magnetic tape (ebay $3-$10)
Tiles measure .75" (19mm) wide x .812" (20.6mm) tall so you can figure out how long a roll of tape you need.
I would suggest unrolling the tape and sticking it to the fridge for a bit to get rid of the curve before you start the project.
I tried cutting with an exacto knife but scissor are much easier and faster too. Just press one piece down at a time, then clip it off the roll. If you try to stick a whole bunch down in a row, when you go to cut them, you'll scape up the side of the tile. Thus why one at a time is better. No wasted tape that way either.