I got this on Chapter 4's first stage, Special Assignment - Kung Fool, which takes place on Barry's dojo, this is easy to do thanks to the amount of Blue and Purple Studs hidden around the stage, keep collecting and looking for them and you'll get the achievement. You will need to achieve LEGO City Hero in every stage for 100% completion, but it will require Red Bricks which you only get later in the game to be easier