I want to build a 2 level oven in aa greenhouse

[Homeshow]

Greenhouse needs heat wood is free. Baking bread and pizza is fun. So why not combine them? Also it needs to have a horizontal chimney for 20' before it turns up thru the roof. The chimney pipe will warm seedling tables. So I'm digging a stairway hole and a flat spot for loading a ground level fire box/oven. Red brick exterior. I would also like an upper chamber with dome for pastries and cakes. What stone for the floor in-between? I need to cut a hole in it to allow fire to thoroughly heat the upper chamber. Along with a removable steel plug. 2 chimney that connect into 1 with gates or bypass doors (terminology?). 3'x5 or 6' with upper door access at ground level on the side.