@ballistic: having worked on the RBC until I left - no, the quick builds at least in the US are a little more professional, primarily for liability reasons. It’s still volunteers but mostly able bodied men, some of them actually professionals and females/older children may provide food.
Where I was, anyone under 18 cannot do volunteer work that is dangerous (eg be near power tools, scaffolding etc), which quick builds are just a slow moving OSHA violation.
The actual quick builds take several weeks now, they have consistently had problems with “too quick” builds and the local media got bored with them and real contractors pointed out the issues - all sorts of things have to “settle” fastening systems, footers, foundations, glues, concrete, cement, the structure was not inspected at time they wanted to do their inauguration etc. There is a reason construction takes time and having to tear stuff back down because you didn’t do or failed a mechanical inspection is more expensive than doing it right.
So about the time I quit, a “lot” was contracted out to some “good ol boys” that surely didn’t need the extra money from the “JW tax”. Off course WTBTS got their kickbacks too. The congregation still got involved but mostly decorations (roofing, siding, painting) after most of the framing and electrical, plumbing, everything else was roughed in, you know the simple stuff your average handyman can do.