It is obvious what effect the diameter of the shell has on the pitch of the drum. Another crucial element involves the material from which the shell is made. Wood is the most popular throughout the world, and synthetic is becoming more common these days. Both materials posses their own unique effects on the sound quality of the drum. Finally, the shape of the drum drastically affects the sound, as much as the holding and playing technique.
Round drums are most common, but in North Africa they have square ones, too.
Embellishing the shell with various elements can give the frame drum a whole new identity and ability to provide a wide variety of sound sensations. Adding jingles or attaching brass rings to a shell would definitely add some spice to the overall sound of the drum, as well as change the way you play on it. I bet you would play it like a totally different instrument. Well, the same kind of effect happens to the frame drum when you add jingles, only now we call it a tambourine. The tambourine family is like an extended family of frame drums.