Hi, I'm totally new to brick ovens, I am gathering supplies right now and then I'm just going to jump into it and get started. It seems like 200 Firebricks will be good (I'm hoping) to make the firing chamber. Anyways, I found this guy who will sell me 4x9 firebricks for $.63 a brick. I'm not sure, but I thought this was a really good deal. Should I just buy like 400 of them instead of 200. Is it beneficial or possible to do a double layer of fire brick? Any advice is helpful. Thank you.