From Command and Conquer Wiki

Due to heavy bombardment from the Soviets the Allies developed fake buildings which were made to deceive enemies into targeting them to draw attention away from their real counterparts. The Fake Construction Yard could be used to asorb attacks from Soviet MiG-29s that may have destroyed their real Construction Yard. These could also be put into out post bases to make them appear to be full bases. Fake structures were not seen in the First War.