A coon squaller gets the coons to stick their heads up too.
What you want to do, is take the reed setup Al sells for the squirrel calls, and blade it heavy like you want to do for a squirrel call. Make it a blow type call with a lanyard, and use a rubber bushing with a half inch hole, because coon hubters are hard on equipment. Its a tough sport.
Make your barrel somewhere between 2 1/2" and 3" long, and make the end fit the hand well, so you can use back pressure on it easily for different tones.
This is a VERY easy caller to make.