The Autobot Earth Base was made out of an old abandoned factory by Optimus Prime's crew after their ship was in an inaccessible place when the came to Earth, light years from anothor planet, and of a need still need a place to call home. It has everything a giant transforming robot could need: a production line, a communications center, and a big-screen TV. There are plenty of extra rooms for the Autobots to occupy in their down-time too, and even one for Ratchet to use as a med bay. About the only thing it doesn't have is peace and quiet so Prowl can complete his Cyber-Ninja training, and it's not really a great place for a small human to live, but, hey, no place is perfect.
What would become the Autobots' base started out as an auto manufacturing plant. Isaac Sumdac acquired it in a merger and, Sari suspected, didn't even remember he owned it.