An improvised ocarina design - to my surprise, it worked on the first try. Cut from a 3.5 x 11.5 inch slab of 1/4" maple. Check the video to hear what it sounds like: http://www.flickr.com/photos/ranjit/5423038441/
With the finger holes on the sides instead of the top, it's not as easy to play as my previous ocarina: http://www.thingiverse.com/thing:1816 - but it's way easier to assemble.
This is part of my project to make a crude musical instrument every day in February. (More at moonmilk.com)
Cut from 1/4" wood or maybe acrylic - I don't know if an acrylic version works, but it probably would. If you cut from 1/8" material, you might try cutting two of each layer and doubling up.
This ocarina was scaled to fit a 3.5 x 11.5 inch piece of wood. It should work larger or smaller, but if you make it much bigger, I suggest reducing the relative sizes of the finger holes so that they're not too big to easily cover with your fingers.
Using appropriate glue, assemble the layers in two halves as shown in http://www.thingiverse.com/image:42408 - it's important that the layers be airtight, so be generous with glue.
Glue the two halves together, and you have an ocarina!