Codes in MA about doing home brew hot water on the roof???

Ya, codes can be a hassle sometimes. Its for a good reason though. I think it has something to do with the "Riot Act." You know, "If we let one person do it then everybody will want to do it and the next thing you know we have a riot on our hands." I am not sure how its on MA but in NC they all fall into the hands of "the Authority having Jurisdiction."
Even national codes.
Which is to say a city inspector might have a different perspective than a county inspector and so on and so forth.
Even city to city. A metropolitan area might stricter on somethings than a smaller city.
A local contractor would be able to answer your questions better I think. Hold on... That darn cat keeps getting out of the bag. Ok, where was I? Oh yeah, contractors of all sorts here in NC must be licensed and have there work permitted and inspected so they would know better than most what the inspector(s) may or may not allow. I am thinking the same is true in MA.
http://www.contractortalk.com/f50/ma-building-codes-59751/
Good luck!