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.
Test Lab Guide: Windows Server 2012 R2 Hyper-V Network Virtualization with System Center 2012 R2 VMM
Even though SC 2012 R2 and WS 2012 R2 are not released yet Microsoft published a guide to setup lab for Hyper-V Network Virtualization. There are no screenshot in the guide but you can have a sneak peak preview of the architecture of the new Multi-Tenant NVGRE Gateway. Check it out here.
Infrastructure-as-a-Service Technical Guidance for Hosting Service Providers
Microsoft published a guide for Hosting Service Providers that use or will use System Center and Windows Server. The guide just gives an overview from which you will be able to get the big picture on where to start but it is useful for starters. Download this document from here.
Updated: System Center 2012 SP1 Integration Map
System Center 2012 SP1 Integration Map has been updated. You can find this cool document here.
Documentation: Cloud Infrastructure Solution for Enterprise IT
If you are designing Public, Private or Hybrid Cloud based on Windows Server 2012 and System Center 2012 SP1 this set of documents will be very useful for a starting point. They will offer you the basics you will need in order to design your Cloud and take the necessary decisions. Download all 4 documents from here.