Isn't a tear down class a potential problem with all the frank'n ARs out there? I do agree that everyone bringing their own stuff in for a build class would be a mess too though.
I'd say that they supply the parts for the build. Maybe you can buy package A, B, or C, but they control what's being brought to the class. Keep it simple, at least for the first class.
I might be interested in just a shorter class to build the lower and then watch the build of an upper.
I would prefer to break the class into 3 days. A day for lowers, a day for uppers, and a day to discuss issues with BCG’s, buffer systems, gas ports, etc., along with general trouble shooting.