The gear box of the gaming / racing wheel that I built follows the simple sequential shift pattern. ie: moving the gear up shifts up and vice versa. For building the gear box, you would need a sufficiently large and stable card-board box. (Go for a plywood box if you can afford it). Make sure that the box has sufficient height so that the gear knob will be at a comfortable position when you start racing. Also get a handle like thing (old joystick handle) to act as the gear knob. The old joystick handle i used has a button on it, so i could use it as handbrake.

This picture shows the top end of the gear shaft that passes through the slit in the gear box of the gaming / racing wheel. As mentioned earlier, two metal contacts are placed at the up and down positions. The metal contacts when made to touch with the metal gear shaft, closes the circuit and acts as switches. Attach wires to both these metal contacts. Notice the colour of the wires so that you wont get confused while assembling the whole thing.

Also connect a green colored wire to the metal shaft. It is always advised to use soldering to connect wires to avoid loose contacts.