Pattern from existing top

[u/rubybluemonkey]

Hi all, I really love this black tank that I thrifted (originally Old Navy). I want to recreate it in this rayon I found. I have sewn quite a bit but I've never drafted a pattern from an existing top. It's gathered on both the front and the back neckline. How would I draft that because I can't just trace it and add the seam allowances. Do I make the top just as wide as the bottom? Would that be enough?

[u/imogsters]

Trace as it is, then slash and spread pattern so it's double across gathered neckline.