i know exactly what you're looking for and they aren't sarong pants, they aren't thai fisherman pants, they are split pants with open side seams from hem to waist.
i'll post a diagram later when i'm on my design computer.
edited here because i'm back.
these are called bali pants, they are sewn together thru the crotch curve and all the rest of the edges are hemmed. ties go on the waist--either as separate pieces sewn on or as extensions to a waist band.
cut the pattern piece twice, on the fold as indicated below.
the waistline of the pattern is equal to 1/2 the total waistline measurement. to be completely accurate, it should be the front-to-back half, not the side-to-side half. the side seam length is as desired. the crotch curve is 10"-11" deep, and 4"-5" wide. the front and back crotch curves are cut the same, you can modify this if you like to allow for a round tummy or round behind.
in this diagram, the center vertical line indicates both the grainline and the side seam. the horizontal line that intersects the grainline indicates the knee depth.
let me know if you have any questions about the draft, how to sew the pants, or how to wear them.