Here you will find as much information as I can give about the various aspects of DIY instrument building.
Where to begin:
Making DIY instruments doesn’t have to be a complicated matter. There are musical possibilities inherent in just about every object you could think of and getting the sounds out of them can be remarkably easy.
I tend to focus on stringed instruments, as that is what I enjoy building. My wind instrument experiments have ended up sounding terrible! So keep in mind I will be talking mostly about strings.
First you need to consider if you want your instrument to be acoustic or amplified. Acoustic ones will need some sort of resonant chamber, amplified ones will need a component that can turn the vibrations of your instrument into electricity (a pickup).
There are two main ways to get your noises amplified, through inductive pickups which uses magnets and coils to turn vibrations into electricity. Or through piezo transducers, which turn ANY physical vibration into electricity. Piezo’s are a great place to start as they are very simple to use and incredibly sensitive, so even if your construction isn’t perfect, you’ll still get good sounds from your pickup.
A lot of the tone of your instrument will come from your strings, only metallic/conductive ones will work with electric pickups so if you’re wanting something softer sounding the piezo’s are the way to go.