I started this yesterday and finished it today. I had a few problems but YouTube helped solve them.
There are many tutorials online for this but the basic premise is this. Measure your waist and add between 20” and 24” which ever gets you to an even number for ease of the maths!
2nd layer is double this 1st layer. 3rd layer double the 2nd layer etc. As each layer is larger than its predecessor, it has to be gathered to fit. Sew into place, iron seams upwards, oversew the edges, iron upwards again to flatten.
Do as many layers as required and do the hem. Make the waistband the same width of layer 1. Height is dependent on the size of your elastic. Mine was about 3” high to accommodate a turn under and the elastic.
The trick to helping prevent your elastic turning over is to allow for a very small seam around the top of the waist band. Thread the elastic, oversew the ends after making sure it fits.
I didn’t make mine quite this size. Top layer was 60”, next 120” and final layer 180”.