Jaxenro,
If you are building a miniature pylon aircraft, I suggest that you do not install a rudder and fly the aircraft using elevators and ailerons only. You won't be using rudder much anyway during high speed flight. In principle one aileron is enough.
For a conventional aircraft (not deltas) elevons aren't very useful, unless you are doing a lot of torque rolling and hovering, in which case the ordinary ailerons are rendered ineffective. Because of the small span of the stabilizer the moment arm will be fairly small necessitating large area elevons or large elevon deflections in order to obtain a sufficient roll rate. Also the bending forces on the thin stabilizer will be rather high.

/Red B.