I was planning to build those for a while now I got a chance to build one. So let's start building.
-Neodymium Hard Disk Magnet
-Bunch of Round Magnets
-Alligator cables (for testing)
-Hot Glue Gun and Hot Glue
-Soldering Iron and Solder
Step 1: Start Making Circuit
First of all I take old usb fan and try using it. But I discovered that it was too fast for this purpose. So I replaced it with brushless pc fan. It give perfect results.
Step 2: Preparing the Enclosure and Assemble Everything
I marked fan and switch on the box then I cut them with rotary tool. Then hot glued everything into the box and also hot glued bunch of magnets for water resistance . Next I painted the fan (Just looks good).