I used the book "Generation T: 108 Ways to Transform a T-Shirt." I chose one that was ruched on the sides. First, I got a shirt that I already had and knew fit well to use as a template. Then I traced a bit larger than that to figure in seam allowances, and a few inches longer so that it could be gathered.
In this design, you cut strips to use as the ruching cord. Then you sew the seam allowances to the outside, and sew them down so that they form tubes to thread the cord through. You weave the cord up one side and out under the arm, then down through the other tube. Then you tie them at the bottom on either side. White trash-a-licious.
The neck holes and the arm holes can stay unfinished, because you're using jersey knit, which won't unravel (the whole book is really based on this principle.) I cut a slit in the top, and sewed a small piece of extended elastic at the bust for a nice little gather. The shirt came out really well, and the evening was a total success, except for the time Al looked right at me and I was singing the WRONG WORDS. He pointed at me, like, "NOW sing that line!" one line later. Doh! I'm sorry Al! I love you!
Incidentally, I didn't post these pictures last year in part because I was afraid they MADE ME LOOK FAT. Um, yeah. And now? I just look at them late at night and allow a single tear to trickle slowly down my cheek.
When this shirt fits again, I'll know the pregnancy weight is off!