>Have you seen that system of building with like large, hollow, polystyrene "duplo" blocks (very quick) then infilling the blocks with ready-mix concrete? Amazing. You could get a house up in less time than it takes your kid to build a Lego Harry Potter Hogwarts

I wanted to use something like that, though these weren't plastic, more like a pressed mix of wood particles and whatnot, like particle board. Couldn't find them when we were building our house there, so we got siporex (which was a brand of concrete foam). Concrete foam is, as they say, "best insulator among the building blocks, and best block among insulators". This means it's not the best possible insulator nor a building block, but the combination is great, specially that we found them at a good price, so we made the walls a foot thick. And the blocks are light and huge, so once you get the knack of it, you can build quite fast. I've built pretty much everything but the ground floor myself - the garage, top floor, windshield wall. And they're very easy to cut.

Haven't found concrete foam blocks here at all.