This paper addresses the problem of how to architect aspects of an Electronic Marketplace (e-Marketplace) to enable Software SMEs (Small and Medium Scale Enterprises) Engineers to easily discover the most appropriate Platform-as-a-Service (PaaS) offerings available in a marketplace. While there are existing architectural models for e-Marketplaces, these models largely ignore the semantic aspects of the descriptions of offerings in the marketplace. In addition, they provide little support for recommendations and decision making for consumers in the marketplace. These shortcomings make the reuse of existing e-Marketplace architectures inadequate for some categories of services such as PaaS services which are characterised by relatively complex technical specifications. We address this problem by integrating a Semantic Recommendation Layer into a PaaS e-Marketplace architecture. Requirements for this layer were obtained from a series of interviews with Software SME engineers and PaaS providers within the context of a Three-year EU Project. We describe the major components of the Layer and the underpinning recommendation and decision model. Results from this work should contribute to domain-specific architecture for e-Marketplaces.