Typically, a reference architecture is a business-ready design with configurations for some common virtualization cases such as virtual desktops or small businesses. It could be, based on use cases, preconfigured, easy-to-order bundled solutions designed to aid in the ordering, deployment, and maintenance of a virtual infrastructure.
You can find several documents from both VMware, usually on specific products, verticals, or use cases, and other vendors where there could also be pre-packaged solutions.
For SDDC design, one of the more complete sources of documents and blueprints is VMware Validated Design (VVD).