I hope I have come to the right forum, but I'm trying to build my own wood-fired oven from scratch. I have no background in building anything like this, so i'm trying to get all the details correct so my oven turns out properly. The question that I have is how large should I build my foundation slab so that my oven is big enough on the inside, and so that there is enough room to add insulation layers? I was planning on digging the hole for the foundation 6 feet wide by 6 feet deep. Is that big enough?