This was a fun little project I did with an old T-Shirt I never wore.
I put on the shirt and put a tank top on top of it, then traced the tank top line with a piece of chalk. (I made the straps a little wider than the tank top's) Then I cut the shirt along the lines in the front and back.
This makes a decent cut top. I could have left it that way, but I decided to keep testing ideas.
Taking the left sleeve, I cut along the seam at the top. (You can cut it further back for a longer braid)
Cut the length of the sleeve into three strips, and then braid them to the end. Then sew the end of the braid to the strap left on the back. I bunched up the strap and sewed further down the back so that it would pull the shirt up on that side.
I didn't like how open the other side was, so I also sewed the hole up a bit at the bottom.
Now I love the way the shirt turned out!
You could try the braid on both sides, or make the thick side a little thinner and keep it from falling off your shoulder.
(Neat trick, if you don't want your straps showing, use a small safety pin to secure them under a tank top.)