Thanks David.
I never get tired of looking at Fallingwater. The house I grew up in (designed by my father - a physician) has some extended cantilevers with inverted beams and tons of rebar. Built between 1965/66 and has never had a sag nor a leak.
When we were building mine, dad's comments were that all concrete work had to be beefier, full soils testing (not a requirement here) and concrete testing had to be done and additional rebar must be added. Our structural engineer agreed with my dad. We had steel trusses made to order in Canada which hold the poured concrete roofs.