They obviously have nothing except the idea. However, you are being wholly unfair to them expecting a prototype. Even with the entire YC funding they won't be able to build more than a scale model, no chance for a working prototype.

This is a very cool, very hard idea to execute - i shudder to think at the kind of testing, reliability and certification you need to ensure a foldable ten-storey building is safe around human crew in gale force winds. It's a moon shot, and sometimes these take you on the Moon.