I really do love modular design. Snap in, snap out customisation. It's something between bespoke designs built from scratch and one-size-fits-all, take-it-or-leave-it mass production. I think about it a fair bit, possibly because I played with LEGO as a kid. And as an adult, though less so. Lately I've been wondering about modular housing. You could, perhaps, use shipping containers for the bulk of the structure, and design individual ready-made rooms with power, water and lighting wired up and ready to go. I don't know how well it would work, but I'd love to see someone try.
Mokalus of Borg
PS - People do build the occasional house out of shipping containers.
PPS - I'm thinking more of mass-produced snap-together rooms to make a whole house.