I hope my suggestion is of help to you and if you do think about making a tier cake then you might want to consider using self raising flour instead of plain flour.
As promised, this is how you make chocolate frosting - very simple
200g milk chocolate / 7.05oz
Approx 50g / 1.76oz butter
2 cups icing sugar
1) Heat the chocolate in a pan (low heat) until smooth
2) While you are waiting for the chocolate, mix the butter and icing sugar together in a medium sized bowl
3) Once the chocolate is ready, add this to the other ingredients and stir well. The mixture should be light and fluffy and easy to spread
You may need a larger amount of each ingredient (than mentioned above), should you choose to cover the entire cake but this will give you a good idea of where to start.