So this part of the costume, the pants, are really easy, but it took me ages to find that out, because I couldn't find any desriptions of the cut of these particular pants (serouel in Algerian) that I never happened to see with my own eyes - all I had were photographs.
The name - serouel m'douar - could have been a useful hint, if I had asked somebody. So the meaning of the name (m'douar means nothing else than "round") became clear to me after a couple of samples that I had tried to make. So here's the description.
You need upholstery fabric which is usually around 3 meters wide. Or you sew a piece which is at least twice as wide as the required length of your serouel (Does that make sense? Lenght: approx 1m; width 2-3m. It depends, how volouminous your serouel should look like and it depends of course on the characteristics of the fabric, stiif or soft, thick or thin).
Now fold your fabric twice.
Cut out a quarter of a circle, or, if your serouel, like in this case, is longer than wide then the waist is the broadest part and the pants become slimmer towards the ankles in a rounded shape. A small piece between the feet is alredy united.
If you unfold the fabric now you should have a
two semicircular pieces eventually connected on the rounded side.
Pleat the waist, or simply gather it (pleats look less bulky).
Se the side seams and leave generous holes where you feet should go (leave at least 40 cm between them, otherwise you will not be able to walk!)