*I have completed the toile for my manikin (exclusive for subscriber), and the result is that I cannot fully fasten the zipper unless I pull up the waistband high up, even though this jean is supposed to be low-waist. I failed to realized that low-waist measurement is significantly longer than the usual waist measurement. So, if you are drafting for real life make sure to add more ease to the waist and hip, or use low-waist measurement instead (about 4-6 cm below waist), except when the wearer has overly protruding belly.
Instruction based on Muller&Sohn "Baggy Jeans" (p134). Some modification to suit my preference.
Not recorded: Watch pocket. Buttons. A lot of topstitches and puckering. In the final garment I add another 2 cm to hem circumference and 4 cm to pants length. Instead of two belt loops at the back, I only put one because I notice most jeans only has one. I use lightweight denim fabric.
If you think it is not baggy enough, you can make the outseam straight down from hip-level, or even curve it out a bit.
The following are my study notes. Download the full scale SVG here.

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Final sewing patterns:

Download link for basic block. The folder name is "Thomas - Muller&Sohn - Basic Block Baggy Jeans 241122"
Download link for 3D files (expire after 2 months).