Nandaimon is a National Treasures of Japan. It is a rebuilt gate. The existing gate was constructed at the end of 12th Century. According to Wikipedia, the architecture of Nandaimon is in Chinese Song Dynasty style. The characteristics of temple in this style are:-
They have two layers of eaves.
The line of upper eaves is curved and with a slight upward to both end.
Of course, the whole structure were made by timber.