Speaking of Star Wars
I'm a sucker for real world calculations applied to sci-fi:
But, before you go off to start building your apocalyptic weapon, do bear in mind two things. Firstly, the two million death stars is mostly from the Earth's core which we would all really rather you didn't remove. And secondly, at today's rate of steel production (1.3 billion tonnes annually), it would take 833,315 years to produce enough steel to begin work. So once someone notices what you're up to, you have to fend them off for 800 millennia before you have a chance to fight back.