It's late, but I told Andrea that I would post a how-to about 2 weeks ago. Hopefully, I will explain this clearly enough -- the being fuzzy headed and tired will get balanced by 2y dd being in BED so I can think straight, LOL.
This is what is a "one-legged" pants pattern in my mental lexicon. You can do this with a "two-legged" pattern, just sew the fronts to the backs at the outseams and start from there...
Here I'm using the knit pants from KSFT, but it works on wovens too, and some patterns call for construction this way.
I serge across the tops and bottoms of each piece first so that when the pants are put together, the edges are already finished. I find that easier than serging a circular waistband/leg. I mark the wrong side of the fabric with chalk so I can keep track of it.
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