For occasional use, don't forget your circular saw. Any old blade turned backwards will readily cut thin sheet metal. Might choose, say a plywood blade near the end of its useful life, but anything will work. Also good for body work. Maybe I will even try the radial arm saw the next time I go to hacking up oil filters.
I learned this trick 20 years ago when I went vinyl and aluminum on the outside of my house. Mostly I used tin snips, but where I needed several pieces the same length, used the radial arm saw. I finally bought a circular saw just to do the gable end pieces. Couldn't cut the edge of the siding on an angle with the tin snips.