I cheated a little with this build and used ebay bought tuning pegs. See my other instructible for making wooden tuning pegs. http://www.instructables.com/id/Good-enough-for-the-bush-Australian-version-of-Tah/step7/null/
How to make a Pocket sized home made Sopranino Ukulele from a plank taken from a shipping pallet.
First find a piece of straitish knot freeish wood about 3 and a half inches wide (90 mm) or more and half an inch thick or more and about 14 inches long or more. I got mine from a section of a plank taken from a shipping palette. A longer plank will give a longer ukulele. I have made a 2 foot long one (which is a Tenor Ukulele) using a virtually identical method and a standard soprano as well.
You can see how they sound here
First is the sopranino tahitian style tuning (apologies for the fat fingers) Second is a tenor Uke tahitian style tuning. Third is a regular tuned soprano uke all made using roughly the same method.