A hatchet and a couple of minutes, depending on how motivated you are.
You're going to go through a thin layer of wood (called "sheathing") and then the shingles. Swinging a tool upward in a cramped attic, while trying not to fall through the ceiling, will be the hard part. The roof isn't particularly tough.
Edited to add: Sometimes experience is the best teacher. I vote that you hack a hole in your roof, then report back to us.