China assembles a 30 story hotel in just 15 days. China builds a 30 story hotel in an unspecified length of time.
edit: Sorry this warranted downvotes. If I were trying to build a prefab home for myself, I wouldn't count the "build" time as time from parts arriving on site. I feel it to be disingenuous. There's a lot more to the process than just assembly of parts. Its definitely interesting that they can assemble things this quickly, but the fact that they can do this is not new. Example: http://news.ycombinator.com/item?id=1911060
Regardless of how much work was done offsite, it's still a unique feat to see an empty lot turn into a 30-floor skyscraper in such a ridiculously short amount of time; there's no doubt it's mentionworthy. However, as others have mentioned here, it doesn't look like anything to cheer about in terms of real quality or durability. There's a reason our methods take longer.
I suppose my point is that it isn't unique, either. They've been doing this for years and there are videos galore including past submissions on HN as I linked.
Furthermore, the 15 days is itself a bit low---notice in the video that by the time the clock starts, the foundations are already done and some parts of the first floor are in; the work continues after the 360:00:00 clock stops; and the last layer of cladding (dark instead of light, which in the finished photos extends to the top) isn't finished past the sixth floor.
edit: Sorry this warranted downvotes. If I were trying to build a prefab home for myself, I wouldn't count the "build" time as time from parts arriving on site. I feel it to be disingenuous. There's a lot more to the process than just assembly of parts. Its definitely interesting that they can assemble things this quickly, but the fact that they can do this is not new. Example: http://news.ycombinator.com/item?id=1911060