My instruments produces sound by plucking the strings or running a bow over the different strings. The vibrations of the strings create waves and out of them sound comes out. The pitch is changing with the thickness of the string and the lengths of the strings. Also the pitch changes when you tighten the strings from the top.
I will use wood and have something to use to model the shape of my instrument. I will need wire for the strings and nails to help with the tuning of the strings. I will also need horse hair so I can use it for the bow.