@nugger I'm not smart enough to predict what sort of tech will win out. It might well be that aircrete big blocks, maybe even made on-site, win out because of better insulation properties, or something different
but yes, basically that. I don't think the McMansion roof is a necessary consequence. If you standardize the dimensions of the room modules, you could have standardized roof sections that fit over it, and the corner piece would just be a corner piece.
It might even reduce McMansionification of the roof to have fewer available combinations