I sewed basting stitches down each edge and in two rows down the middle of the fabric to hold the pleats in place. Then I cut between the two rows of stitching in the middle using a rotary cutter.
I added piping and a flat section of fabric to the top of each pleated piece, then stitched. See how to make your own piping here.
Then I just sewed it together like a regular zipper pouch, like this tutorial.