@nathanu Look at the Paramount Trail Convertible Pants from North Face.  I'm a bigger guy like you and I'm always looking for a roomier cut when I backpack as well.  I just got some of those North Face pants, and they're fantastic!  I've had them out on a few hikes already and they move so well with me.  There are a few products out there that are lighter weight, but with these I don't have to worry about ripping them out from the slimmer cut.  Plus I'm a big fan of convertible pants, they're very versatile.  Full pants or full shorts, or you can even partially unzip the legs to dump heat but still keep on the pants legs.  Check them out.  I got mine from Amazon and I'm very happy.