What should my Doumbek drum be made of?

I am very interested in the cultures of the Middle East, especially the music. I have decided to try to learn how to play the doumbek so that I can experience this a bit more fully. However, I am not sure which type of doumbek I should buy. I saw a copper doumbek for sale, but I have also heard that they are available in a bunch of other materials, including aluminum, and I am not sure which is better. Which type of doumbek is best for beginners? I don’t want to spend a ton of money on my first drum, but I want a decent one.