I have to agree...if customers are allowed to sauce and cheese their own skins...you will be overwhelmingly dealing with way too much sauce and cheese. First, most people are unaware just how little sauce is needed for a pizza.....AND they will, almost to the man, try and "get their money's worth". This will lead to a huge number of pies coming out "soupy". AND, if I know customers the way I do, they will blame the lousy pie on.....YOU.
As Craig pointed out, you concept is basically the hottest pizza concept right now.......a FAST CASUAL pizza place. I also agree that 800* is the poster boy for a well done version of this concept. (They are however, expanding AND adding groceries AND an old style italian deli to their menu).
AND, Craig ALSO was correct is saying that all these places seem to be on the west coast. I've looked into the idea....and frankly, i don't know if it would fly here in New England. Too many Italians, too many good pizza places. But, I admit, people seem to be open to the idea. BUT, give some serious thought to letting customers getting involved in production.....and I don't even want to THINK about the health department overreactions.