Hells advise is top notch. Get hold of as much reference material as you can. Also if you know someone who has one, then he/se is weird, but ask if you can borrow it LOL.

Seriously tho, go to a museum if there is one nearby that has one, study it and imagine it as it is, but made out of the basic primatives then you an refine and model it out to suit the needs of your project.

Hope this helps.