I made my vest pattern using one of my t-shirts as a template.
I pinned the shirt down on some cardboard and traced the shirt out. After I cut out the cardboard template, I used that cardboard pattern and traced it out on a larger rectangular piece of cardboard. What I had to do was place my template near the bottom of the rectangular cardboard and after tracing that out, I flipped it over(like turning a page in a book) and connected the template "shoulder to shoulder" with the already drawn out pattern and traced out that pattern as well. What you'll get is a pattern that'll give upper shoulder room and connects the front and back vest. I did have excess on the sides of the vest which you can trim,sew together, zip, ect. I used industrial velcro on my sides and they conceal very well. It also permits me to suit on or take off my vest by myself. There will be some trimming involved just to get it right but I don't think it will be much. As far as the shoulder pieces, I used cardboard templates again and taped them to my vest. Get a good look in the mirror while wearing your vest and/or helmet because it helped me to gauge the right proportion so that everything looks correct to the vest. I had to do that several times. When you find the right look, trace them out on your material and add them on. I hope this helps out some and good luck!