The gamepad was designed in EagleCAD and available to download and modify. It's also a shared project on Oshpark.
Let's start assembly by putting the gamepad together. Gather up 10x 6mm tactile buttons and a 40pin IC box header.
To make it easier to insert the buttons to the PCB, use a pair of flat plier to straighten out the four leads of each button.
Now is a good time to tap the mounting holes of the gamepad PCB. We need to create threads on each hole so that it's easier to mount to the case. You can use a #4-40 sized tap tool, or a #4-40 machine screw to do this, just make sure to fasten as straight as you can.