I've said something similar to this before, but it's amazing how many of these creatures and contraptions were actually built. These are real schematics for building R2-D2. This is the thing that would have needed to exist in the real Star Wars universe. Someone would have gone through all the same steps that the visual effects team went through to create R2-D2. Of course the Star Wars universe would have a could of extra steps, like building the working inside instead of a hollow base for a little person to climb inside of.
There's an actual R2-D2 that you can build piece by piece that I saw while I was in the UK. It's not a simple recreation. It's very detailed. I think there are at least 12 packs of pieces which require not only model-making skills, but electrical skills as well. Very cool stuff.