pleats are easy to add to a pattern, if you already have a dress pattern that you want to work with.
just take your starting pattern and draw a couple of *straight* lines where you want the pleats to be (the lines need to be straight and follow the grain of the fabric, or the pleats won't hang properly):
cut your pattern along these lines, and spread the pieces out so the pattern piece is almost three times as wide as it was to start with (no wider than that, or the pleats will overlap each other and get all bunched up):
the blue dotted lines are where you will fold the fabric in the next step.
cut out your fabric, and pin it right sides together along the red dotted lines. loosely baste the fabric along the red dotted lines, all the way from the top to the bottom, then stitch with your machine along the red dotted lines, starting from the top, going down only about 3/4" (or longer if you prefer).
press the pleats flat, stay stitch across the top through all layers of material (this will make it much easier to sew on to the other pattern pieces). when you're done, remove the basting thread (the red dotted line) and voila! pleats!
one tip: pleats look best in a fabric that will hold a crease well, like wool.