I made this top myself without any instructions, I think I did okay. And it helped me realise making clothing isn't too difficult. It's just a matter of getting the right shapes and the right sizes (no matter if you're making from an old T-shirt or from scratch)
Sorry for the bad quality on some of the images!
Firstly put the T-shirt on and place a mark just below the bust (I used my bra as a measurement)
Take the shirt off, Mark a line accross the shirt and cut along this line
(don't worry about the seam allowance, it shoudl work out okay)
For the moment we're working with the bottom part of the top, so put the rest aside.
You will need to measure your hips divide by two, maybe add an inch for comfort and then add and inch for seam allowance.
From one side measure this along the top mark a line parralel from the side and cut along this line
I'm sure you could measure just under your bra and minus and amount of inches to get the right amount of elastic, but I just put the elastic around me and cut what felt right (remember it needs to be a little smaller than you so it holds it's place)
turn the top inside out and put the elastic along the inside.
Pin it down and sew
fold the elastic over and sew again
Now, working with the top part.
fold in half and cut off the sleeves
cut from the edge of the neck line to the bottom corner and the parallel from the start of where the sleeves start to curve to the bottom.
Now you have the top parts
Se up the open edge of the bottom
Place the top parts so the edge touches the folded edge of the bottom of the top.
Pin and sew (make sure just to sew the one side)
Do the same for the other side.
And you're done. Wear it with pride!
(and maybe a little bit of body tape :P)