Play the tune on only one string. Leave the other string open, as a drone string. Box Drum First came the hollow log. Then the large slit drum, which evolved into this portable version. Fine hardwood makes a much better sound than plywood.
Hardwoods have a very nice sound.
Any size will work nicely. A coping saw is best, for the blade can be removed for cutting the inside shapes. With the saw, cut on the lines drawn. Using one or two drumsticks or a mallet, tap the different areas of the box for different tonal patterns. This makes a soft, bell-like sound.