Drew's right. Don't just cut your floor on a whim. Make sure you have a pattern. You prolly already knew that. Leave as much good original material as possible. I used a cutting wheel when I did mine. Much nicer cut then the gorrilla boogers from a torch. Also, since you're making a flat floor and I had to choose between 16 or 18 guage sheet metal, I would most certainly use the 16 guage. In my opinion much easier to work with then the 18, plus it'll be stronger.
Have fun!
