Shown here are 3 of the body types you can get. Skinny, medium build, and body builder. Most artists tend to stick between skinny and medium. Its difficult to get a head to look right on a very large body, and its not typically 'pretty'. But don't be scared, experimenting is key!
Tip: See how the different muscles appear as the character gets bigger? Some bigger characters have more built arms, or abs. Once again, the medical diagrams will help you understand.