here are the complete primaloft pants for inspiration: Momentum shell and liner, 0.6" of primaloft sport, and full #3 molded tooth side zips. 11 oz on the not so accurate spring scale.
For fit, I made each of the 4 panels wider on the outside (where the zippers are) by 1.5" per panel, so for each leg it was 3 inches more in circumference, which is only about 1 inch more diameter. do not add width to the inseam and crotch seam since that might mess up the fit, especially in the hip area (ie adding an inch all the way around each piece would be 4 inches wider in the legs, but above the crotch it would be 8 inches wider. Not good.)
I then proceeded to check the fit and trimmed off about half an inch of the 1.5" I added, so it has an inch extra (on the outside edge of each panel, for a total of 2" extra diameter per leg). I also sewed the crotch seam a little narrower.
*** this was done for a looser fit that could fit over winter clothing for backcountry skiing, so they could fit smaller for pants that get used mainly for in camp at night