Its my boyfriends birthday this weekend and i realy want to make him this cake. Any ideas or tips..?
How many people do you want cake for?
I'd go small; about 5x7 inches on an 11" board: I'd stack about 7 cake layers with a tough filling like ganche, if you go for a bigger cake you'll need internal supports at the 4th layer.
then do a thick ganache crumb coat (about 1/4 inch thick) on all sides- let that firm up in the fridge and then cover with black fondant. after that the little details should be pretty easy.
if you want to make the guitar get some gum paste or make/buy some modelling chocolate/candy clay. if using gum paste (GP) start it asap as it will need time to harden. cut out a rough shape, let it dry overnight then neaten any rough parts with a sharp knife then colour using gell colours and dipping solution or vodka - if you mix the colours with water they'll make your GP sticky and it'll take ages to dry - dipping solution dries in seconds.
Hope that helps!
Have fun baking!