I saw the tactile buttons on a fidget cube, and thought that might be nice on a slimmer pad that you can slip into your pocket easier than a cube. A bit like a handy piece of bubble wrap you can pop, but it doesn't run out.
You will need 8 6x6x7 tactile switches. Just snip the metal pins off them, and push into the provided holes in the base. Push the printed buttons on top of the switches, and finish with the top cover. A drop of superglue in each corner helps keep the cover secure.
A little sanding might be necessary depending on the tolerances of your printer.