I'm by no means an expert, so take the following advice with a grain of salt and, as you should always do, make a muslin before you cut into your good/expensive fabrics.
I think the picture is of "cowl pants", and here's what I would do:
1) Take a pattern for trousers that fit you. (Front side on the left, back side on the right).
2) Choose how low you want the "draping to be", make horizontal lines at the desired depth, and make curved lines from the waistline, to the side, as shown.
3) Cut up your pattern through those lines.
4) Arrange them so that the top parts form sort of a horizontal line, with some distance between them (The distance being two times the depth of the "draping", the more distance, the fuller the pants will be). Arrange the rest of the pieces so that the waistlines become curves, and the bottom corners are touching. Turn the hem lines into a curve. (Explaining this with words is hard, just look at the image
Now, I'm not exactly sure whether you should cut this cross-grain, or with the grain running vertically, maybe someone with more experience can help, or just make a couple of muslins and see which one hangs best.
To sew them up, just fold it down the middle, and sew the top (going from the waistline down to the middle point), which means you'll have a seam running down the side halfway down the leg, not all the way to the hem, and then sew the rest like you would any other pair of trousers.
Hope this helps! Best of luck, and do post the results if you make them
Source: Adaptations from instructions for a "cowl skirt" in Winifred Aldrich's "Metric pattern cutting".