I got inspired to do this piece after watching Ninja Assassin. If there's something I've learned from working on this drawing is this: I love Google Sketch Up! It saved me a lot of time with the architecture and perspective (and, technically, it's not cheating since I had to build the whole thing myself - I see it as inking my own 3D model.) I was surprised at how user friendly the program is, too. It can be downloaded for free here.