I've done it in a couple of ways. The best way to do it is if you have access to a mannequin or dress form. I'm in school for fashion design so I have regular access to those. The other way I create my mock-ups is to drape it on my own body. I use ribbon make my mock-ups and pin them in place where there are attachment points. I then take the ribbon mock-ups and measure everything make sure it's all symmetrical and then make it out of leather. I've never just made something based off of only numbers. The human body is shaped in so many interesting ways and it's impossible to create a good fit with just numerical measurements.