Sorry for the shabby drawing--I'm a visual learner, so I thought some may appreciate pictures, no matter how sorry looking! :)
This project is better suited for those with some sewing ability. While it isn't what I'd call "hard", I can see where it is not exactly a beginner-level endeavor. But don't lose heart! If you have a knack for sewing, certainly give it a go, if perhaps on a toddler scale. I constantly surprise myself--you probably will, too!
These instructions are for an adult-sized pirate shirt. Scale it down accordingly for children or toddler sizes.
1. Use a button-down shirt that fits your buccaneer as a pattern guide. I'll call this shirt the "guide shirt". The pirate shirt will be pulled on and off over the head, so don't use a tight shirt or a shirt made of stretchy fabric as your guide shirt.
2. Close the shirt front (i.e. button the buttons). Turn the shirt inside out. Tuck in collar and sleeves, and smooth out all the layers of material as flat as possible. Fold it in half at the middle (where the buttons are), so that you're looking at half a shirt body.
3. Get a width of material twice as wide as the full body of your guide shirt. Fold it into 2 layers (one wide of shirt body). Fold in half again (half the width of the shirt body). Lay your folded guide shirt on top of your folded pirate shirt material, lining up the folded (middle) edges. Cut out around the shirt, leaving an inch for seam allowance on the edges. This can be cut down later if it's too big, but you're better safe than sorry by allowing more fabric than you might need.
*You may want to make the shirt longer than your guide shirt, to allow for a belt or sash at the hips. This is especially the case if your pirate will be wearing tight leggings--cover up that booty! Consider this when cutting.
4. Unfold layers. You should have 2 identical pieces that look like the body of a shirt. With right sides together, sew together the shoulder seams and side seams. Be careful not to sew your arm or neck holes closed.
*You may want to leave 4-5 inches open at the bottom of the side seams for ease of movement, if the shirt falls at or below the hips (which it probably should in any case).
5. Designate one side as the front (shouldn't matter which). Trim the front neckline lower than the back by two inches or so. Cut a straight vertical line, about 4-5 inches long, down the chest of the shirt, beginning at the middle of the neckline. This will be the slit that laces up the front.
6. Make sure it fits your pirate, and make any necessary adjustments; take in the side or shoulder seams as needed. Finish the bottom edge.
Now you're ready to go on to the other parts of the shirt!