Honestly he's asking for a guide, not your opinion on which car he should purchase next, whether he should cause a fatality by making his car turn in the opposite direction or your opinion on the 'coolness' of the modification.
First off if you don't understand basic wiring principles and electrics I would advise you NOT to do this.
On the ignition barrel you have 4 or 5 wires (4 I think) 3/4 of them are positives and one a ground, each stage you click the ignition grounds another positive thus first of all turning to ACC1, ACC2 and then finally engaging the starter motor.
You need to be in ACC1+ACC2 to even start the car so you would have to either turn ur key to the stage just before starting or have a switch to turn ur car to ACC2
Then it's a simple case of starter motor wire goes to ground and it attempts to start the car.
+ve *starter button* +ve > Relay Coil side > -ve
Starter Wire > Relay Latch side > Ignition Ground
Where i have put starter button you would just snip the wires for the horn and use that as your switch.
If you can't follow this guide then you aren't experienced enough to do the modification and I would sudgest getting a professional to do it or just not doing it at all.