Like its Green Zone counterpart, it will be gigantic, at least by the standards of Washington's diplomatic community, having at least 250,000 square feet. The next-largest of the 15 embassies in the new International Drive complex are the embassies of Nigeria and Malaysia, at about 100,000 square feet each.
From the article linked above:
Although the Embassy was designed largely in the West (by Chinese-Americans I.M. Pei, Li Chung and Chien Chung), it is being built by a consortium of four massive companies from the East: the China State Construction Engineering Corporation, the Shanghai Construction Group, General Corporation and China Rilin Construction Group. Many of these construction giants have been involved in building the gleaming new Chinese skylines of cities like Shanghai. Secrecy and security have been paramount concerns on the construction site in Washington. Few visitors have been allowed inside to glimpse the building’s progress. The construction site’s gates are monitored night and day by watchful Chinese guards who carefully inspect every shipment and container entering or leaving the compound. Virtually every worker and contractor has been brought in from China or somewhere outside of the United States, and virtually every step in the design and construction phase is inspected to ensure that no "unexpected modifications" slip through. There is virtually no local content in the entire edifice.
If I didn't know better, I'd think that the Chinese have been taking Fortress Embassy lessons from the U.S. State Department.