Grab one or two t-shirts (The number of shirts you use depends on the the size of the shirts and how long you want your dress. I used on 3XL shirt to make mine)
I you use one shirt cut it into two pieces. One piece should be long enough to cover your upper torso (at least) and the bottom is whatever fabric is left.
If you use two shirts, you can leave one shirt as is and cut the amount of fabric you want for the bottom from the second shirt.
Turn the top piece inside out and cut off the sleeves and collar of the neck.
With the shirt still inside out Take each flap around the neck (there should be four! Two in front and two in back) and fold them down about an inch and stich them closed with a whipstich. This should create a casing about an inch big on each flap which will be used to hold the string of fabric for the straps.
Fold the bottom of the top portion up about an inch and stitch with a whipstitch. This will create an inch wide casing for one of the two stings of fabric that will be used the cinch the waist.
Take the piece of fabric that will be used as the bottom of the dress and turn it inside out. If the bottom portion already has a hem on it (like mine did) then you do not need to stitch a casing, and will instead use the hem as a casing for the second waist cinch.
If the bottom portion does not have a hem, then you will need to create a casing for the second waist stitch in the same way you create the casing for the top portion in step 4!
Leaving the bottom portion inside out and the top portion right side out, place the bottom portion over the top so that the right side of both portions are facing each other.
Pin the two casings that are to be used for the waist cinch together and attach the bottom to the top using a whipstitch (take care that your stitch is not too big or you may stitch the casing closed and not be able to fit the strings through in the next step)
Fold the bottom portion down!
Take extra fabric from one of the shirts or use fabric from a third shirt and cut three pieces of fabric about 1 to 2 inches wide.
Take one of the pieces and attach a safety pin to it. Thread this piece through the casings on the four flaps around the neck.
Take the other two strings and feed one through the casing on the top portion for the waist cinch and feed the other through the bottom casing/old hem on the bottom portion
Be careful not to pull the strings all the way through because then you have to start all over again which is extremely frustrating!!!
Tie off the waist cinches and the string around the collar and try on!!!