You might think that the soprano marimba is the place to start.  And in many ways I would agree...it's the first marimba I started with and making it first has some advantages.  For one thing, it is smaller and lighter than the tenor marimba, and therefore easier to move around.  It is also cheaper to make because it requires less materials....and significantly, it is easier to tune.  The soprano generally plays the tune so you feel you have made good progress when you have one because you can show others the capability of the instrument and give a hint of what might be achieved in time.

 

That said, once you have a soprano marimba, making other marimbas to play alongside it may be more difficult if you haven't fully taken into account the availability of the materials you will need to make bigger, lower register instruments.