Let me show you how to make your own caftan, and you will not need a pattern.
Step 1: Measuring and Cutting
Fabric, at least 1/3 yard more than is needed for the main body of the caftan (mine was a light weight denim with the stripes woven in. I found it in my fabric stash.) Note: satin has wonderful drape.
Cloth tape measure
Sewing machine (although can be tediously stitched by hand)
Wash and iron the fabric.
I folded the fabric in half lengthwise and held it up to see if it would fall long enough. I held the folded edge on my shoulder ,and the fabric fell to about mid-thigh. I wanted a longer, but the fabric was wider than I needed, and I used some of the excess to lengthen the caftan.
Then I measured for the width of the entire caftan. I took my cloth tape measure and held the zero against my spine and measured to my elbow. This was 18 1/2 inches. To this measurement, I added 1 1/2 inches for hemming.
If the fabric you plan to use is less than 45 inches wide, you may need to add band of fabric to each selvage edge. My fabric was 60 inches wide; I had to cut off the selvage edges (and used them to lengthen the caftan and for the neck facing.)
I folded the fabric in half lengthwise and then in half again across the width. I measured 20 inches from the center width, and, lucky me, I found a stripe line there. I cut straight along the stripe line through all four layers of fabric.