Some of the links on this forum allow SMF, at no cost to you, to earn a small commission when you click through and make a purchase. Let me know if you have any questions about this.
1/4" seems to be the standard. Don't go cheap or you will be hating life in a few short months. You might be able to get away with 3/16", but even cutting the 1/4" she will want to curl a bit on ya. There are some very talented and much more experienced builders on this forum that I'm sure will be on shortly to help answer any questions you may have. Good luck to ya, it's an exciting time isn't it ???
1/4" is about the perfect thickness for a build. Sturdy, but not to heavy to work with. And it will last a life time if you take care of it.
One thing I've been thinking about doing on my next build, people talk about insulating the firebox and all, ...was maybe double up on the top plate of the firebox leaving about 1/2 inch gap between the two plates. Most of your heat is lost through the top, it would help keep the heat even on the reverse flow plate. and help save the paint on top of the firebox. I always thought insulating the whole box was overkill, but think doing the top would be worth it.