BIG CULOTTES-PANTS have side pockets and elastic waistband with a casing.
Sew in-seam pockets (Illustrated tutorial HERE). Finishing seams with bias binding strips provides a clean and beautiful inside.
Form the pleats along the front and back waistline, following the direcion of the arrows on the pattern. To balance the seams, cut bias stripes of the same facric and sew them together with the seams., then, press seam to one side and the added bias stripes to the other, as if it was an open seam. The pressing will be perfectably balanced. This technique is used both to balance seams on pleats and darts. Here for demo I used a contrast fabric.
Stitch the waistband vertical seams (on the round), leaving a small opening between the notches. This opening will allow inserting the elastic later. Fold the waistband in half lengthwise and press.
Stitch the waistband to the waistline. The vertical seams of the waistband should march the pant´s lateral seams. Turn the waistband to the inside along the fold-line and turn in the allowances., then stitch-in-the-dich from the right side, along the waistband seam, so the allowances are caught between all layers.
Insert the elastic.