Ross Crawford’s brick ukulele can be played and its four strings are tuned to C, F, A and D.
This model has to be able to withstand the tension of 4 fairly tight strings without exploding. I ended up using a pre-stressed Technic rod up the middle of the neck, which allowed the head to be securely attached to the body, and it works really well. The body (briefly described above) ended up being very strong, but I had to use a saddle attached to the lower end to get enough strength – the saddle I originally designed was attached to the front, and was only able to tune the top string to about B. The final design allowed me to tune it to D (still way short of a real uke, but good enough for me).
[Via The Brothers Brick]