THAT would be awesome. But, where will the resources to build such a thing come from? Interstellar mining will need to be done in order to harvest enough materials to build a custom planet. A good way this could actually be done is to put a strong center of gravity in the asteroid belt. Asteroids will be pulled towards it, and will slowly form a a proto-planet. After an even longer time, it may become a full fledged planet. Of course, this will take probably a billion years.