It started out as an idea. Then it took shape, growing and expanding and changing until it more closely resembled the solution you had in mind. Do everyone a favor and write it down, won't you?
Maybe it's just a series of blog posts on your progress (or lack of it). That's a great place to start, especially if you get some good feedback from your readers. Take some pictures of your work along the way. It's entirely possible that the idea you discard will be the perfect solution to someone else's dilemma.
If you don't write it down, it didn't happen. Make something happen today.
Now let's move on and look at the tools and techniques you need to design, build, test, and program your own Arduino creations.