In my 40+ year career, I've probably been involved in building around 10 data centers.
Then this article was mentioned in Windows Weekly episode 721.
Microsoft currently operates more than 200 data centers. Think of the logistics of building 50-100 data centers each year! I'd guess there would have to be 10-20 people dedicated to each project not to mention the expenditures.
After each data center is up and running, then you've to facilitate the network connectivity, the power, the operations, etc.
In this article was a link to a virtual tour.
PS. The article mentions that few people ever get to tour Microsoft's physical data centers. I was fortunate enough to tour Microsoft's Redmond facility in the mid-2000s. The thing that made the longest lasting impression on me was a single server they had over in a nook in front of a glass window. They described that as a "generic" server. The idea was that any manufacturer could build a server to those specifications and the hardware would be interchangeable. In hindsight, no manufacturer wanted that as it would be too easy to displace them but the idea eventually manifested as virtual machines that aren't tied to a hardware specification.