I’m building this and reading this. Projects with concrete are so damn cheap–the only problem was I had to carry a 50lb bag on my back for a half mile.
I’m on my way to learning how to prototype with actual code (always the best method in my opinion) but wow Omnigraffle is a good stopgap. Here’s a blog post on how to link layers to make pretty fresh prototype. It’s an expensive tool, but it’s awfully powerful.