Once you complete the game, let the credits rolls. Once they finish you will be transported to a miniature version of the city that you get to wander through and destroy. Once it is destroyed 100% the achievement pops.
As you are destroyinig the city, you will collect studs and your combo multiplier will be in effect, so you will get multiplied studs which means you should also complete :
Master of Collection - Reach True Ninja Level 20
if you haven't already.