I have designed arcade buttons for a DIY project of mine. The design is very simple and uses commonly known tactile switches as seen in the pictures.
I have only tested the buttons with the 6mmx6mmx5mm diameter.
6x6x4,3 and 6x6x6 will probably work too.

A source for 6x6x5mm buttons:
https://www.amazon.com/CO-RODE-Tact-Button-Switch-6x6x5mm/dp/B00W0YUV1W

A hole with a 15mm diameter is needed for the installation on your project.

Enjoy!