I made this from a size L t-shirt that I loved but never wore. Five Iron Frenzy was my favorite band, and I missed a concert but gave somebody money to buy me a shirt. They came back with this (I never remember to take pictures before I start), but it was too big.
I traced an American Eagle tank I liked, and came up with this:http://geocities.com/dooneyfrenzy/craftster/smurffront.txt
and here's the back:http://geocities.com/dooneyfrenzy/craftster/smurfback.txt
start with a t-shirt (obviously)http://www.geocities.com/dooneyfrenzy/craftster/tutorials/cct01.txt
do this kind of thing to it:http://www.geocities.com/dooneyfrenzy/craftster/tutorials/cct02.txt
If the sides fit you fine, then you don't have to mess with re-sewing them, but what I did is cut the shape I wanted out of the front and a wide rectangle out of the back, the height of one side of the front:http://www.geocities.com/dooneyfrenzy/craftster/tutorials/cct03.txt
I sewed them together on one side, put it on and figured out where to sew the other side. I then had a fitted tube-ish thing:http://www.geocities.com/dooneyfrenzy/craftster/tutorials/cct05.txt
Cut two strips about 2" wide out of the rest of the shirt for the trim. Cut all the way through the shirt, the trim piece needs to be long.http://www.geocities.com/dooneyfrenzy/craftster/tutorials/cct04.txt
Put the ends of the two pieces together (right sides facing) and sew to make one LOOOONG strip. Doesn't matter how long, just LONG.
I'm sure there's an easier way to do this (and I'd love to hear it), but fold the strip in half (right sides facing) the long way and sew to make a tube. Trim the excess material and turn it right side out. Fold this strip in half with the sewn part in the middle and iron it flat. Basically, you've just made your own bias tape. Sorry I don't have pictures for that step.
Now add the trim to just the very top part:http://www.geocities.com/dooneyfrenzy/craftster/tutorials/cct08.txt
I cheated at this part and used fabric glue with my pins, since I neglected the ironing part. To add the trim, put the edge of the fabric inside the fold and pin. Then sew across it. I did mine twice because the first time, some of the trim came out from under the needle in the back and didn't get sewn down. I was tired because my neighbors woke me up with their stupid party, and I didn't know what else to do since I couldn't sleep. But in the end, I liked having the two lines there, it looks more professional.
Next you're going to find the seam of the long trim piece, where you sewed the two strips together. Start pinning that dead center of the back, and use up all your pins as you continue pinning the trim piece to the tank.http://www.geocities.com/dooneyfrenzy/craftster/tutorials/cct09.txt
(Make sure you have enough bobbin thread) Start sewing at the end of one strap and go all the way to the end of the other strap.
Next, put on the shirt. You could even cut the straps and leave it as a halter top, or you could have someone safety pin the straps where they look good and carefully take the shirt off and sew the straps to the back.
I thought about using a snap or button to make it into a 3-in-one deal: tie the straps behind your neck, attach them straight to the back, or criss-cross. You might want to try that... who knows?