Inspired by a dress I saw at TJ Maxx, (I think it was Cynthia Rowley), I grabbed a couple of tshirts from my stash and created this:
Aside from the wonky pleat detailing (which, if I make this again, I will spend more time trying to do it right - I did this while the kidlet was napping), the only thing I hate about it is that I didn't cut the neck binding down, so I had to make darts at the top so it would lay flat.
How I did it:
The main tshirt body was a plain black tshirt. I removed the neck binding, then folded the shirt in so the center front and center back were the sides. I measured in 2" from center front, and cut straight down, leaving a four inch gap.
For the pleated part, I took the second shirt, cut the back off into a rectangular piece 2" longer than the length I wanted the pleated section on the finished shirt. I pleated it lengthwise until it was 6" wide. Securing the top and bottom of the section I wanted to use for the pleated part, I then sewed against the pleat, holding each pleat open against the grain while sewing. Alternating rows of with the pleat, against the pleat. I then took another section of the spare shirt and added length enough to the pleated part to = the length of the shirt + hem.
Then I attached the pleated part to the original shirt, then attached the neckband from the second shirt.
I think I'll try it again with another shirt, taking more time on the pleating, though.