Ruffles can be added to to circular skirts or panel skirts.
Make the basic 4 panel skirt pattern. Decide how wide you want the ruffle. Subtract that number from the total radius.
If the total radius is 20 inches or less, 1⅛ yards of 40 inch wide fabric can be folded into quarters and the waist line cut from the folded point.
If the total radius is 28 inches or less, 1⅔ yards of 60 inch wide fabric can be folded into quarters and the waist line cut from the folded point.
Make the ruffle one inch wider than you want to so that there is a ½ inch seam allowance at the top and bottom.
The length of the ruffle should be 1½ to 2 time the the circumference number at the bottom of the skirt pattern.
Note: I usually make the ruffle longer than I really need, and then run a section through the ruffler until I get the effect I want. I ruffle the entire strip and then sew it to the skirt.