Here are the complete steps toward building a 3-stringed musical instrument, taught and inspired by the Andy Mackie Music Foundation. the instrument has a dulcimer's tuning, and sounds & plays beautifully. I teach a musical instrument building class to public middle school students in the adjacent high school wood-shop. Here, students have built dozens upon dozens of guitars, of various shapes and flavors. I shall make best attempts at teaching you my techniques, including what works well and areas needing improvement. Students get to bring home their finished instruments, such a joy to see their pride in ownership!
Step 1: Start with a Stick!
When choosing your stick, make sure it is planed evenly on all four sides, doesn't bow or bend, and is straight & true!
I use "instrument-grade" wood such as mahogany and black walnut. Once I built one out of a African wood called bebinca. All our wood is donated to the Andy Mackie Music Foundation, for the purpose of teaching children to make and play their own musical instrument.
If acquiring these kinds of wood is just not possible, heck, then try using what is available to you, such as ash or another type of non-instrument-grade wood. The reason I suggest ash, is that it may bend more easily in a future step. Experimentation is most encouraged!
Here the measurements can vary. If you want to make a wider one to accommodate more than three strings, that will work too! Our kids have made many with varying lengths, including 12 inches longer than 30.5 inches, as well as shorter "ukulele-sized" instruments with less of a fretboard range.
Noting the direction of grain is important, such that when it is time to cut the fret wire grooves, the saw slices perpendicular to the grain.