Building 5 of Science Department of Peking University is the first floor of Yifu, located on the left-hand side of the southeast entrance, next to Joule East, north of Deba Qiu, diagonally opposite Yingjie Exchange Center.

See the figure below for details:

Image source: Peking University Alumni Network

Supplementary information about Peking University Science Building:

Peking University Science Building was completed and put into use in 2000. It is a modern building complex integrating teaching and scientific research. The construction of the Science Building was strongly supported by Sir Run Run Run Shaw, Chairman of Shaw Brothers Co., Ltd., who donated 42 million yuan to support the project.

The science building in Peking University includes the first floor of Shaw and the second floor of Shaw.