What you will need:
Fabric of your choice
Existing pair of shorts that fit you well
1. Fold your fabric in half to get two layers (if you have a print and orientation of the print matters, fold accordingly so when you cut, the print isn't upside down). Take your existing pair of shorts and fold them down the center seam. Lay it on top of your fabric and cut a similar shape out of your fabric, accounting for seam allowances. Use the picture below for an approximate reference of how the shape should turn out.
When you cut the center seam area, begin to follow the curve but stop about halfway and then cut straight up. For the waistband area, leave more than the width of your elastic band above the waistband area to account for the casing we will make later.
3. IF you want to make hidden pockets in your shorts, you can follow my tutorial to make pockets in my skirt tutorial here. Pay attention to only the side seams.
If you don't want pockets, head to step 4.
4. Starting with two pieces, right sides touching, sew up your side seams and inseams together. Repeat with the other two pieces.
Hope you enjoyed :)