What is tofu-dregs construction?

It refers to poorly constructed buildings.

https://en.wikipedia.org/wiki/Tofu-dreg_project

A tofu-dreg construction, or tofu-dreg project, is a poorly-constructed building, sometimes simply called a "Tofu building". First used by former Chinese premier Zhu Rongji in 1998, the term refers to the dregs leftover after making tofu. The term was used prior to this to refer to any poorly-done work. Buildings and structures such as these have been a problem in China for decades, particularly during the 2008 Wenchuan earthquake, when schools collapsed, killing student within them.

https://en.wikipedia.org/wiki/Tofu-dreg_project