A basic tester is no more than a neon bulb with a series resistor. I have no idea what the mains voltage is at your location or how for example residential power is wired? So a basic tester is a neon lamp and a series resistor and a more detailed tester would be three lamps and three series resistors.
Here is one example of an AC Outlet tester. Beyond that, more information would be needed as to exactly what you want.
Then post a few of your ideas and drawings. Then work from there but at least make a few basic drawings based on what you think will work for you.
Ron