This is how I made my pantaloons; your mileage may vary.

materials:
+ about 3m of silk brocade (115 cm wide), which I bought because I liked it, but without a project in mind
+ a chunk of contrast fabric for the yoke and cuffs (used less than 1m)
+ a chunk of flannel for interlining (used half as much as the contrast fabric)
+ drawstring

starting out:
+ cut the fabric into 2 lengths, each 145 cm long, and full width (each piece had 2 selvages)
+ cut the yoke pieces (simply a rectangle of contrasting fabric, big enough to cut down to size later)

pleating to the yoke:
+ calculate dimensions of pleats (decided to make 20 pleats to make the math easier), allowing 2cm on each side for seam allowance
+ iron the 'front' edge of each pleat (the fold that shows on the outside when you wear it)
+ pin near the edge of each fold so it doesn't unfold as I work
+ mark the yoke with the finished located of pleats
+ pin each pleat to the yoke
+ pin the living crap out of the rest of the fabric so nothing is going anywhere
+ press
+ sew, being sure to remove every pin before I drive over it
+ add inside layer of yoke and interlining, press
+ topstitch yoke along the pleats

determining yoke placement and pant length:
+ figure out most flattering location for pleats to start (I like it roughly in line with or just above the crease at the top of my leg)
+ figure out length of pant leg by tucking the bottom edge into socks or string/elastic and blousing it out
+ cut bottom edge (this removes the selvedge) (reserve fabric for gusset)

pleating to the cuffs:
+ determine size of cuff (big enough to get around my ankle with an inch or two of overlap)
+ sew cuff up like a waistband - sew on three sides (outside layer, inside layer and interlining)
+ pin pleats in place and sew as above
+ press seam allowance under on wrong side
+ topstitch from front, catching seam allowance on wrong side
+ attach hooks and eyes as a closure (or simply pin in place for wear)

legs and gusset:
+ put on pantaloons and pin legs together from the ankle up, leaving a gap for the gusset
+ experiment to ensure mobility and attractive drape
+ make a gusset that matches the gap (gap will dictate the length of gusset; be sure to make gusset wide enough)
+ insert gusset and sew up leg seams (I used French seams throughout because my fabric frayed like mad)
+ sew yoke pieces together at front and back

finishing yoke:
+ put on pantaloons, hold in place with wide elastic, fold remaining fabric over
+ arrange yoke as desired and mark the fold at the top of the elastic (this is the finished top edge); it's often most flattering to have the front waist slightly lower than the back waist
+ make a casing and add drawstring (I like to make a drawstring out of the same fabric; a bias tape maker is especially handy for this - even though you don't cut the fabric on the bias for a drawstring)