The bodhrán constists of a wooden rim or hoop about 16 - 18 inches (40.5 - 46 cm) in diameter. the hoop is usually about 4 to 6 inches (10.5 - 15.25 cm) wide and the wood is usually about 1/2 an inch (1.25 cm) thick .   
The hoop usually has one or two cross braces in it for added strength and to use as a handle, although some players prefer none.   
The brace is usually about the thickness of the players wrist away from the skin.   
some newer bodhráns are made with a laminated hoop which is quite strong and does not require a brace for strength.   
Over time many different skins have been used to make a bodhrán, i have used and/or heard and/or read of sheep, calf, goat, deer, greyhound, donkey and kangaroo skins.   
Traditionalists seem to have settled on feral goat skins.   
the most desirable characteristic of a good skin is thickness.   
a thick skin is less susceptible to changes in temperature and humidity.