Hi Edge,
While I agree with Marcos recommendations,unfortunately when I built my oven I was unable to find specific directions on how a novice like me could actually build an oven?The site I quoted you was for IMO the most informative available.I did however adjust my design somewhat from their directions (hearth size,position of chimney,dome width etc)You are free to adjust the design as you wish.Certain dimensions/ratios are important to understand in the oven design.Maybe Marco will expand on his information ,and advise you of the ideal method of insulation and material,what material to use for the chimney pipe and exact construction methods/dimension et. for his recommended oven design.Unfortunately for those of us limited to the English language,trying to find out specifics for building an authentic Neapolitan oven is somewhat difficult and seems shrouded in secrecy!Indeed it may even be beyond an amateur like me and I believe there are only a handfull of truly capable builders out there today.If you check this forum, I think it has been said that even ovens built in Italy have had to be demolished as they did not perform as desired. The only other thing I would say is to put a lot of thought into it before you lay a brick.Persevere and have fun.You will find lots of opinions out there and will have to sort through them and decide what you want,are capable of,and materials/information available to you.Marco is a knowledgable source.Someone like me needs a specific step by step-"paint by numbers" almost guide.I had never laid a brick before,but am currently satisfied with what I've achieved.Good luck
David