This is a recycled-t-shirt skirt I made for a friend. It's a tiered, patchwork skirt. The pattern is adjustable for however much fabric you have (within certain minimums).
Step 1: Harvest Fabric
Cut them all into rectangles. Mine were mostly six inch squares, but you can introduce some variation in width as long as the height of each rectangle is the same.
Step 2: Lay It Out
The important thing here is that the top piece is about the size of your waist (so if you have a 25" waist, your top row should be 25" across). You will lose some fabric to seams, but that's good because the fabric is stretchy and it will make a secure waistband.
The other important point is that the width of rows should increase as you approach the hem of the skirt.
In the picture, the right side is the top of the skirt and the left will be the hem.