The first thing you need to make your own pattern is a swimsuit that fits. I used this one because it fit my daughter perfectly.
I like to cut patterns on the fold, so the first step is to fold the suit in half. Pinning helps keep everything flat and even. I also pinned the bum inside so I could trace better.
To draw the pattern, I start with a straight line. This will be placed on the fabric fold. I find craft paper to be really great for cutting patterns. This roll I bought at the Dollar Store.
Trace around the suit exactly as it is. We'll add the appropriate seam allowances in the next step.
Since we'll be adding 3/8inch elastic to the leg opening, I added a 3/8inch seam allowance. The easiest way to do this is to simply lay the elastic along your traced line and trace again.
I added a 1/4inch seam allowance on the side and 3/8inch along the top and armhole.
Most bathing suits have the crotch seam offset to the back, so we have to add that on to our front piece.
Lay the bathing suit on the pattern as shown and trace. Add the seam allowances....
and you've got a pattern!
Do the same for the back.
Keep in mind that crotch seam again.
Cut out the pattern pieces you've created and double check that the side seams are the same length. You might have to make some minor adjustments.
Check the crotch seam as well.
There you have it. Pretty straight-forward.