How to make my own atx power switch?
The requirements for the switch are not severe. The switch will be pulling down a current-limited 5V signal. It should be normally-open and momentary (non-latching).

The motherboard manual will have diagrams of the pin headers; two of those pins will be for the power switch (one side for the signal, the other for signal return / ground).

A reset switch is always a good idea too - the same sort of switch will do (momentary, normally-open).