During Valentine's Day season, a whole bunch of craft and style blogs did round-ups of special, handmade ladies undergarments. I kept my eyes open for an article on underwear for the gents, but it never surface.
So I did some research, and this is best of the free how-tos out there.
It's from a Japanese site devoted to all kinds of underwear making, and includes an elastic waist and button fly.
The free, downloadable pattern and cutting guide are particularly helpful. And they include a special trick for a curved hem for the fellow with strong [big] legs.