excellent advice from my brother-in-law, who excels at modeling, among other things (like protecting his family from rabid cats in Haiti, becoming my personal blog photographer, and bike trials)
Pajama pants are great for all kinds of activities, like sleeping, yoga (for bonus points, make a matching bag for your yoga mat!), washing dishes, baking, surviving an earthquake, walking the cat.... If you don't already have a pair, you should make one. Or four. I made four.
With all that experience, I can tell you that the fabric for pj pants is great. I chose cotton flannels, and made a navy pair with little mooses, one with a blue cowboy theme, a pair with a hilarious print of bears, tents, and camping equipment, and one in a beautiful beige and tan plaid. Check out all the cotton flannels, and find something with a sense of humor.
Everyone makes pajama pants patterns - except maybe Vogue. I bought Simplicity 2541, because it comes with men and women's versions of the pattern, and includes pieces for a pajama shirt -- that, come to think of it, I am 99% sure I'll never use. But it seemed cost effective at the time.
The pattern is very easy to follow, and produces a great pair of harem pajamas if you don't cut down the length above the crotch by an inch or two... or probably three, for a woman's pair. (Seriously, this pattern is long in the crotch to pigeon-smuggling proportions.) Don't forget to add the length back at the bottom of the leg when you cut, or you'll end up with pajama capris.
I'm fresh out of clever things to say about this project, so get thee to a sewing machine to earn yourself a nap and the pants to do it in.