*I apologize in advance for my wrinkly fabric*
What you will need:
Fabric of your choice (preferably lightweight)
A tshirt that fits loosely on you
Optional: pins (necessary for step 6)
1. Fold your fabric twice to get a total of 4 layers. Next, take your tshirt and fold it in half down the center. Align the fold of the tshirt with the fold of the 4 layers of fabric. Sketch a tshirt shape out using your own tshirt as a guideline (include seam allowances). Leave plenty of fabric at the bottom to cut your high-low hem later. Cut on the lines you drew.
2. Unfold your fabric- you should be left with two identical fabric pieces shaped like a tshirt. One of them will be the front piece and the other will be the back piece. Take one of those pieces and fold it back in half again. *You are now working on your front piece.* Deepen (not widen) the neckline on this piece by roughly sketching out a lower curved line. Cut the neckline out.
*TO BE SAFE, I would not suggest cutting the fabric like I did. Don't lay the front piece folded on top of the unfolded back piece in order to avoid accidentally cutting into the back piece.*
Depending on how long you want your high-low hem, you can curve your line less or more to get your desired length (i.e. end your curve higher or lower on the raw edge).
4. Take your back piece and fold it in half. Lay your folded front piece on top of your folded back piece. Note: you should have two separate folds aligned. Just like step 3, start from the fold but at a low point and curve upwards this time. Your curve should meet with the front piece on the raw edge side. Cut out your back hem.
Once again, depending on how long you want your high-low hem to be, you can adjust where to start your back hem line on the fold. The lower you start, the longer your back hem will be.
5. Open up both your front and back pieces. Lay the open pieces on top of each other, making sure the right sides are together (i.e. the sides of the fabric you want people to see in your finished product are facing the inside). Sew along the areas marked red below.
I chose to do a subtle high-low, meaning my curves aren't very deep. If you curved the front piece more (rounder) and started curving the back piece from a lower point, the high-low effect would be more noticeable.
6. This step is optional but if you would like to get the illusion that your sleeves were sewn in separately, keep reading! If not, skip to step 7. This is my way to cheat and make "sewing" sleeves in easier.
I've tried sewing the sleeves on separately before and I found it very difficult. However, I also don't like how a shirt looks if the sleeves appear continuous with the entire shirt. With your shirt flipped inside out, pinch ONLY the front piece where the seams would go if separate sleeves were sewn on. Pin that area so that you end up with a pocket of fabric sticking up. Sew the portion that was pinched. You should end up with a part of the fabric sticking upwards. Repeat with the other side of the front piece and back sides (you should be doing this a total of 4 times).