as for how long to cut the denim, i just cut to where i went directly under the lowere tip of the pocket. this way i could still have full back pockets. now, on to those squares.
as i said earlier, i had a lot of cotton fabric leftover from making my circle skirts and wanted so badly to do something with it. so, i took the five different patterns and cut out 5"x5" squares. of course i didn't cut out the same number per each fabric b/c i had more of some fabrics than others. in total though, i cut out 147 squares...but my skirt only needed 136. this number will differ for each person, especially if you want to use use more or less for each row, and how long you want it to be. as you can see, that was A LOT of cutting, and this where you'll be glad to have a rotary cutter, if you have one! another useful tool is a serger. not saying you HAVE to use one, but it'll def make the project easier and go faster. my serger saw lots of work this project, b/c every stitch is serged. the only time i used my sewing machine was to make the gather stitch on each row. so once i had the squares cut it was time to start constructing the skirt.
to get the first row of squares, i measured the width of my denim. in total, the circumference was 40", give or take, so i knew the first row of squares needed to be bigger than that. so, for the first row i used ten squares, making the row 50" long. once you have your squares selected, you'll sew them together to create a tube. since it is bigger than the denim, i had to gather the top of the squares row to make it fit. to do this, i set my stitch on the longest stitch setting and turned my dial to a higher number. for instance, my dial goes up to 9 and i set it to 6 (the higher # you set it to, the tighter the gather will be). this creates a gathering effect as your fabric goes through the machine. start at one point sewing around, and as you get back around to that starting point, stop a little ways before you get to it, that way if you need to adjust the gathers as your attaching the layers you can.
once you have your tube of squares, with right sides together, attach it to your denim. i pinned every row to the previous before serging to make sure everything fit correctly. now you can serge, or sew, the two edges together. when you reach those pockets on the back, you'll have to unstitch the pocket so you can reach the denim edge to attach your fabric. next, you'll repeat the steps for making the rows, creating the tube, and gathering for each row. for each row i did, i did eight rows total, i added two more squares to make the row bigger than the last. *ex: my first row was 10 squares, so in sequence i did 12, 14, 16, 18, 20, 22, 24.*