oh hey you can definitely do that
i've been finding a lot of books on that lately actually, it's called "flat pattern design"
you buy a basic bodice pattern, basic sleeve, basic anything
I read almost all companies will have one.
and you alter it till it fits you the way you want it to.
after you can use this basic pattern as a foundation to create other designs
So you could do this, so it would be of use to you later on
Or you can just go ahead and make the pea coat... which I searched for on burdastyle.com. I found a couple of links but it directed me to google or some other page really fast... not sure what that was about.
I wasn't able to click the links