I got the idea for these jeans from the so called "jeggings," particularly the tupe that has elastic at the waistband (the jeans in the picture are the "Jem" by Goldsign (photos from madisonlosangeles.com)). The way I went about it was to trace a pair of very skinny jeans I have, compare it to a leggings pattern, and take it from there.
Much like with any other project, finding the right fabric is critical, and it is NOT easy to find lighter-weight denim with suffucient stretch, good recovery, and nice soft feel (not if you are a home-sewer, anyway). For this project I requested some samples from http://www.lurasfabricshop.com/, but while I'm waiting, I decided to repurpose some never worn stretch Target bootcut jeans.
I am not sure why I bought the Target jeans in the first place. While the fabric weight and wash are nice, the pants were always big on me. To make things worse, the topstitching was gold lame - just awful, so I had to remove all topstiching ( had to keep the gold hardware, although I wish it was not gold...). Also, every single -seam, but the front pockets was undone.
Next, I positioned my pattern so that it works with what I had and with the back pockets position (had I moved the back pockets, marks would have been left on the fabric). Next, I did all the topstitching of the pockets with navy blue thread, removed the zipper, and closed the front closure for good. I did completely new outseam, inseam, hem, and back crotch. The front crotch seam from the original pant seemed to work, so I let it be.
For the waistband I used 3" wide waistband elastic from Joann (really good quality, actually, soft and does not roll). I cut it to the desired length, marked it at quarter points ( marked the pants accordingly), and sewed it to the pants. The original waistband was discarded.
That was pretty much it. The undoing of all seams has the tip of my fingers paining and worn out. On the upside, my husband asked when I had bought the pants, and I take this as a good sign.