(I don't speak Italian, sorry.)
It really depends on what you're trying to do exactly. Does adding different parts only change the rocket's appearance, or does it also change the rocket's speed and behaviour? Do you want the player to be allowed to arrange the parts however he wants, or should he only be allowed to arrange them in ways that make sense (i.e. there are certain parts just don't go together)? Should the player be able to remove parts later in the game? All these questions would affect how you'd go about making it.