Draping Period Costumes
If you are comfortable with flat patterning, an easy way to create the pattern for the Cotehardie is to use the pattern you have just draped for the outer layer of the Doublet. Trace around it and add the desired extra length to the bottom. Take into consideration the added flare needed for the hips. Sew the garment slightly outside the seam lines so it will fit over the doublet.
You can also drape the Cotehardie over the padded doublet on the dress form. Use the same method as used for the outer layer of the doublet. Instead of stopping at the waist, continue down until you reach the desired length. The Cotehardie will open in the front.