
(By Philip Larson; the Forbidden City)
First of all, the Forbidden City is impressive in its scale, and its architecture emphasizes horizontality and monumentality.
But in Gyeongbokgung Palace, proportions employed are less severe or overwhelming.

(By Philip Larson; the Forbidden City)
Again, very horizontal and wide tendencies can be seen.
(By Philip Larson; the Forbidden City)
The first three photos are taken from the Forbidden City. Notice, the color of roof tiles is orange/gold. In Korea, no such color was ever used for a roof.
Also, the walls inside of Forbidden City were colored in red; in Korea architecture, walls were never colored in red.
(By Philip Larson; the Forbidden City)
(By Ken Douglas; Gyeongbokgung)
These two photos compares a "Gongpo" (Dougong in Chinese; the wooden bracket system used to support the weight of the extended roof) of the Forbidden City and Gyeongbokgung.
The proportions are vastly different between two structures.
The example found in the Forbidden City uses a "Dougong" that is quite small relative to a massive horizontal beam underneath. Actually, it looks more like a decoration.
However, in Gyeongbokgung, this "Gongpo (Dougong)" is quite large and pronounced.
Notice again the use of colors. Chinese used colors that are different from Korea's "Dancheong." (The term used to call the coloring of Korea's buildings)
(By Philip Larson; the Forbidden City)
Another element that distinguishes traditional Chinese architecture is the frequent use of bricks in buildings' construction.
Please observe the wall on the first floor of this building.
These brick walls were created, covered with a plaster (? I am not sure) and then painted in red.
In Korea, bricks were rarely used for a building itself. Every building in Gyeongbokgung Palace was made out of wood (except for roof tiles and other details), and they stand on a foundation made out of stone.

(By Philip Larson)

(By asmythie, Flickr ID; Gyeongbokgung)
This comparision also shows the difference between Korean and Chinese architecture. In China, these dolls (called "Japsang" in Korean) show more details, but in Gyeongbokgung they are very abstract.
Also, Koreans applied white, block-like decorations along lines where two opposite sides of the roof meet. This use is quite unique to Korean Palace architecture.