The Construction Yard is the most important building in bases. It allows various structures to be set up and allows for storage of resources. If the construction yard is destroyed in an attack, your entire base is destroyed.
A second Construction Yard (which is also a second base) can be acquired by purchasing an MCV through research. With each upgrade, more slots are gained, making base building more strategic.
Construction Yards begin as level 1 and must be upgraded to access any building above the Harvester.