Keyboard wiring?

Does anyone have information on building a supplimental keyboard for a
computer? I'm going to be using a DOS-based program for my DRO readouts,
and would like to build a keypad with big buttons (like 1x1" monster
buttons, probably will be membranes as well) for the most important
functions (zero axis, change incremental/absolute mode, etc) so that i dont
have to worry about hitting the wrong button or getting cutting fluid or
chips in my laptop's keyboard and the keypad can be mounted to the mill.

Thanks,
John