And here’s the first dress I made the same way: http://wornthroughshoes.tumblr.com/post/25595486345
*This is my first attempt at a tutorial so be forewarned.
(The numbers correspond to the captions of the images)
First find a dress that fits well with a simple bodice. (1)
Then take the oversized button up shirt and take the sleeves off and completely apart (with a seam ripper to save fabric). Then use the fabric from the sleeves to make the back sections of the dress (the bottom row of image 3). Do this by pinning the fabric next to the seams and then cutting, allowing about half an inch all the way around for the dress seams. Then do the same with the front piece of the bodice and the top of the button up shirt (2).
After you cut the front piece out of the shirt then cut all the way across the shirt to make the piece for the bottom of the dress. After that use the remaining fabric to cut the front side pieces.
Then pin the pieces together (try them on to ensure it fits properly, 4) and sew them together. After this take a piece of elastic that fits your waist snugly and make a casing for it (the casing can be a different fabric if you don’t have enough of the shirt left over, the casing should be twice the size of the elastic plus at least an inch for the seam allowance and room to sew it to the dress and should be long enough to go around the bottom of the bodice plus an inch) pin the casing to the bottom of the bodice so that one edge lines up and the extra inch hangs off the other side (5) and then sew it on as close as you can to the casing’s top edge.
Then take the piece for the bottom of the dress and gather it until it is the same distance around as the bottom of the bodice (7) then pin it to the bottom of the casing and sew it on as close to the casing’s edge as you can.
Put the elastic through the casing sewing it together and then to the extra inch of the casing (this should tuck into the other side of the casing when the dress is on).
Then make straps, attach them, and add another layer to the bottom if you want more length.
P.S. Sorry if this is hard to understand, feel free to message me and I will try to help or answer any questions.