Will roof work done by unlicensed volunteers pass code?
You are going to have to call your local city hall.  They will tell you if you need to pull permits and what checks there are.

As for "roofing" - there is no roofing certification so in theory anyone can put a roof up.  The church's insurance might not like this but if the city signs off on it or doesn't care than put up the roof.  

I would highly suggest that you get a local roofing company and let them know of your situation.  Most would be willing to take on a smaller profit for having a foreman out to a site with many volunteers.  

I am not sure what the height and slope of the church is though.  With a steep peak this might not be doable.  Just a lot of variables here.  And you don't want someone getting hurt and there being no church left.