Measure from where you want the top of the dress to sit to where you want the bottom of the top part of the dress to sit (A). Now measure from the bottom of your bust to where you want the bottom of the dress to sit (B). also measure around your waist, halve it and add a few cm for hemming and seams (C). Cut one of each (AC) and (BC).
Now measure across your bust (D). Cut one that is (D) long and the difference between (A) and (B) wide.
Gather the ends a little to add shape
Sew the bust part to (BC) and then sew that to (AC) leaving one side open.
Now decide how many layers you’d like the dress to have and how long you want each layer. Pin each layer together and with your sewing machine on the loosest stitch, sew all the way along the fabric.
Very carefully gather the layers so they fit along the bottom of the bodice. Pin and sew
Now pin the zip all the way down and sew it, then sew up the rest of the seam. And you’re done :D