From DT Online
This Ocarina is based on a 'Icosahedron', a geometric solid made from 20 equilateral triangles. You can design your own based on other forms, such as the dodecahedron found in the non-cuboid section of D&T Online. Smaller sizes will give high notes and large ones low notes. The length of side on the Ocarinas can be varied to experiment with different ranges. For a Soprano try between 25mm and 30mm side, Alto between 35mm and 40mm and Tenor between 45mm and 50mm. The largest you can get on an A3 sheet of card is about 65mm length of side. The size and position of the finger holes is a matter of personal choice. You will need 8 holes to produce a full octave.