I cut out rectangles of denim. They are stacked top tier, middle tier, bottom tier. They get a little wider with each tier also. The top and middle tier have 2 pieces, the bottom has 3. 
Then I serge the rectangles together to make loops. The bottom tier I also serge the bottom edge for the hem, and the top tier gets serged for the waistband.
Serging done!! That was the easiest part...
ok, so this part isn't hard, just time consuming, and invariabley, finger poking. Pins.... lots and lots of pins. I run two basting lines on the edge that needs to be gathered, pull to gather, and pin in place. Now, on the cotton dresses I make for the girls, this is insanely easy.... I discovered I should have used a heavier weight thread for this denim... my thread groaned, but didn't break. A major shout out thanks to Ingrid for helping me gather the bottom tier... I was mega-procrastinating...
Now its' all gathered, and I stitch a 5/8" seam between my two basting lines. Easy as pie. I have Michael remove the pins, then pull the basting threads, then serge the seam, nice and secure.
ain't that nice?
I iron the seam up, and top stitch it so it lays nicely. 
I don't do this for the cotton skirts, but I thought it was really needed for the denim or Natasha would have those seams rubbing her leggs all the time. How annoying. I know the stitching barely shows... that's the point, isn't it? ;-) 
turn, iron, and stitch the hem. This only needed a 1/4" hem, so that was nice and quick.
Almost done!!!!
Turn, pin, and iron the top for the waistband. I did a 1 1/4" casing, since my elastic was 1". 
sew.
Don't forget to leave a hole so you can insert the elastic!!
Cut the elastic to length. I run it thru, then pin it so she can try it on before I finish...
this helps it not move, so I can pull it out and cut any adjustments...
ok, so it was 3 tries and 6" of adjustments...
I use a vertical stitch so the stretch isn't compromised by my stitching. Tuck it in, stitch closed the hole, and stretch the waistband to even out the fabric around it.
Last thing I did was to put in 4 verticle seams, one at each side seam, and one middle of the front, and middle of the back. This will help prevent the elastic from rolling, and from shifting the skirt around too much.
And here we are! One finished tier skirt or prairie skirt!
