Hope I’m not too late here…
I’ve made the vest a few times, and up to and including size 5 (from memory) you can cut the vest from a piece of 44inch fabric folded that is the length of the vest length. Beyond that size the vest becomes too wide and you’d need to double the amount or rotate it 90deg and buy as much fabric as the WIDTH of the vest pattern piece. I hope that makes sense.
You need quite a bit of fabric for the vest if you’re going to create your own double sided quilted fabric to cut the vest from.
For those sizes I mentioned I’ve made it from1 metre cuts.
I’ve used 1.5metres of lining fabric and that’s allowed me to make the bias binding for the vest from the lining fabric. It kind of ties the vest and jacket together.
This blog post may help you visualise what I mean:
http://bartacksandsingletrack.blogspot.com.au/2013/07/a-pattern-to-make-product-to-be-proud-of.html?m=0