[splitdisk]

I'll admit that I too have dreamt about doing something like this, but more along the lines of adding a sub-basement beneath an existing one. Almost like a Cold-War era bomb shelter, or safe room. Doing so on public property is obviously a bad idea for a number of reasons. Also barbecuing in an enclosed space-great way to win a Darwin award.

[chiph]

Even on your own land, if you go too far your city's code inspectors might get involved.

http://www.kvue.com/story/news/local/2014/05/25/2435656/

[splitdisk]

Yeah, it's likely a terrible idea to start "modding" a pre-built home without consulting builders, getting the correct permits, etc. There's probably few non-nutcase reasons why a person would do this, as your link attests to. Still, a man can dream about having an indoor shooting gallery, or whatever. The best option would be to construct from scratch.