You're going to need some pieces of sheet metal to build the box, aluminum or steel works. a small LCD screen, some kind of microcontroller board, wires, a soldering iron, the most important part though is the homo sensing antenna. They're hard to find. They need to be made of a special gay sensing alloy. If you do some searching for gay sensing alloy you should find it.
After that it's a simple matter of building your gaydar box, wiring the LCD and the gay sensing antenna to your microcontroller then a bit of programming to get the results.
It's an easy project. It can be put together in a couple hours once you've got the parts.