Blair,
I've been making calls for more than 20 yrs. If your making a cut and glued box call the sides should be about1/8thick, maybe a bit thicker 5/32 or 3/16, you'll have to experiment.,thinner makes it raspier and lower in tone wood choice makes a lot of difference in thickness needed for good sound. a good place to start is with an internal sound chamber about 1and1/2 deep by 4 and1/2to 5and1/2 long, about 1and1/4 wide at the top of the box, 5-6 degrees angle on the end blocks.the paddle should be about 1/4 to 3/8 thick the thicker the higher pitch.Shape your radii for the box and paddle on the belt sander. Mahogany and poplar are the easiest to tune, cedar and chestnut are also good choices.
Hope that helps.
Kevin