Database as a Service is not one of the most popular services but for sure it is gathering more and more usage. It is difficult service to design and built so for sure this architecture guide from Microsoft can help a lot.
If you are working in one of those companies that are building IaaS there are two guides from Microsoft to help you with the basics. Check them out:
Here you can find a download link to the new Data Warehouse Architecture Diagram. Thanks Travis for sharing.
The Microsoft Private Cloud Fast Track Program is a joint reference architecture for building private clouds, which combines Microsoft software, consolidated guidance, and validated configurations with hardware partner computing power, network, and storage architectures; and value-added software components.
The provide documents can be very useful in designing Private Cloud Solution based on System Center 2012: