I did a free hand Iron Man MK3 Space armour from the comics this last summer and I find the best way to do it is simply reference the piece your building draw out what you feel the shape is trace it to either card or brown bag paper, test it against yourself (or other parts if its raised such as the shoulders) then try again. do it three times or so then pick the one that fits best and move on to the next piece. its slow work but better then making a foam piece gluing it on then finidng it doesnt fit!