Start with your oversized Tee.

Then cut off the sleeves. You'll need these later.

And the neck.

Now cut a gradual slope starting at the bottom corner and going up to the used-to-be armpit.

Turn the whole thing inside-out and match up the sides.

Now sew up the edges. You don't need a lot of seam allowance, because the material doesn't fray.

Here's your seam.

For the triangle top, cut the sleeves where the bottom seam used to be. Now you have a sort of trapezoid shape. Cut a triangle from the sleeve. the bottom should be where the finished edge is.

Cut another triangle from the other sleeve in the same fashion. I recommend extending one of the bottom corners a bit so that the two triangles can overlap some.

Sew a seam on the two unfinished edges.

Now, back to the body of the dress.

Fold about an inch and a half down at the top of the skirt. This will make a casing when you sew it all together.

Then turn it inside-out, keeping the fold in.

Take the two triangles and lay them out the way you want them to be in the finished product.

Now take the two triangles and flip them so that the wrong sides are facing up. Center them along the top of the skirt so that they overlap where the fold is on the other side.

Sorry, kind of confusing!

Pin the triangles in place. The pins should go through the folded piece, the skirted piece, and the triangles.

Turn it back right side out and sew, first along the top of the folded part and then along the bottom. Now there's a tube.

Here's the tube. Now take the pins out.

Now you need to salvage three strips. I got two from the back of the old neckpiece and one from the front.

Cut one of the strips in half and sew the other two together, end to end.

Now you have all of the fabric ready.

Sew each of the shorter strips onto the top of the two triangles.

Then cut two slits in the back of the casing. Using your safety pin, (which is pinned to the end of your long strip), to thread the string through the casing.

Now tie the strips behind your neck and pull the drawstring tight- you're all done!