I started with this pink shirt (Gap Outlet, $3- years ago) that was too big and I've never worn it.
(mess = trying to decide what other shirts to re-purpose)
I put a favorite shirt that fits (Target a few weeks ago) on top to use as a pattern and cut the sides leaving a bit for a seam allowance.
Then I cut the bottom edge off this cream shirt, to make a 2 1/2 inch wide strip. I gathered it into a ruffle and pinned and sewed it onto the pink shirt.
I also cut the collar off the white shirt to use as a new neckline to cover the fraying top edge of the ruffle piece.
Since the pink shirt was too big, afterward I also adjusted one of the arm straps so the neck would lay flatter. I'm likin' it.