How many square yards of waterproof leather would it take to fabricate my own top for a chop top 84 s-10?

I recently bought an old truck (84 s-10) that some one owned as a toy and they converted it to a chop top. I've looked up some already made tops but they are way out of my budget. So I have decided to just fab my own. I've come up with my own ideas on how to seal it up using the leather but the only issue I have is trying to find out how much leather I would need. there are plenty of places that sell it online by the square yard. so my question is how would I find out how much I would need or how would I measure it out myself?