MSN Sankei's IZA [Japanese] has an article regarding prefabricated Japanese-style rooms.
Traditional Japanese-style rooms have tatami mats on the floor and sliding doors called shoji and fusuma that surround the rooms, but newly constructed houses in Japan don't necessarily have Japanese-style rooms, as life-styles of young people are getting Westernized. When they want to have Japanese-style rooms after they purchased houses, they have to spend much money to re-form rooms. The prefabricated Japanese-style rooms are for such people. By purchasing the prefabricated ones, they can construct Japaense-style rooms in Western-style rooms. According to the article, the companies that developed the prefabricated rooms also have plans to sell them to foreign costumers.
You can see some more photos of the rooms in the following pages. Unfortunately, they are only Japanese-language Websites;
I could not find any English-language Websites for the prefabricated Japanese-style rooms. JETRO has an English language description on the prefabricated room.
Wa-Koubou, GUU (和工房 寓):
--- room 1
--- room 2
--- room 3
Sakamoto Otozou Shouten (坂本乙造商店):
--- Room 1 (You can scroll down the page by putting the mouse pointer on the arrows at the right side)
--- How to build room 1
---- Room 2 (narrow one, 1840 mm x 1845 mm)
---- How to build room 2