I made one years ago using a turtle shell that I found and a piece of slate that had come out of another call. I glued it in with Gorilla glue, as I recall. I liked the way that it looked but frankly, it did not have very good sound.
There is probably someone on here who really knows how to do it properly and can give you much better advice. I did enjoy the project and it was one more way to make something that had some personal meaning.
"If he's out of range, it just means that he has another day and so do you."