Built this Mattone Barile Grande over the summer. Took longer than estimated but I was doing the work on my own because of social distancing.
I am in Vermont so I went with a frost protected floating slab for the base. Up top, I went with a poured in place hearth slab because I was going to have a hard time finding people to help me lift the three slab sections into place.
The width of the hearth slab had to be increased by 4 inches to account the added dome insulation that is recommended for cold climates (I included some thermal images to show the great job that the insulation does). I also increased the length of the hearth slab by a couple inches to make sure that there was room for the brick exterior enclosure that I went with and the 6 inch lip that is needed for the door.
I have to say, the posts and pictures in this forum were very helpful in getting everything figured out, especially with any variations from the traditional plans. Hopefully this post can help others.
My family has been using the oven every weekend for pizza and other meals, we are excited to keep using it into the winter!