You'd also be surprised to the extent at which it's possible to have datacentres within datacentres. Separate data rooms, or floors within the building can have different power, UPS, HVAC specifications (i.e. to a customer's requirements). Often, a datacenter provider might sign a over a proportion of the space to a large provider, and they essentially become an anchor tenant for the facility. The anchor tenant may even be involved during the build out phase to negotiate the spec etc.