Most Lego Hulkbuster Armor builds focus on size. Most of them end up towering over the official Hulk figure. Although there is a certain charm to seeing a such a massive Iron Man, having a more proper scale version is awesome. Over on Lego Ideas, Ka.Lor has proposed their version of the Hulkbuster. By not having to design a full pilot cage for an Iron Man Minifigure, Ka.Lor is able to focus on mobility and structure. The end result is a Hulkbuster that is amazingly tiny, yet still incredibly imposing. Some of the details here are great, such at the Lego binoculars being used for fingers, Minifig hands being used for various clips, and even tiny Lego pistols being used to define the chest shape.
Check out, and vote for this Lego Hulkbuster over on Lego Ideas: https://ideas.lego.com/projects/58065
There is also the Lego Iron Man: Hulkbuster Project over here: http://legogenre.com/the-iron-man-hulkbuster-project/