Smart buildings as human-cyber-physical systems (h-CPSs) are capable of providing intelligent services, such as indoor positioning, personalized lighting, demand-based heating ventilation and air-conditioning, and automatic fault detection and recovery, just to name a few. However, most buildings nowadays lack the basic components and infrastructure to support such services. The investment decision of intelligent system design and retrofit can be a daunting task, because it involves both hardware (sensors, actuators, servers) and software (operating systems, service algorithms), which have issues of compatibility, functionality constraints, and opportunities of co-design of synergy. This work proposes a user-oriented investment decision toolset aimed at handling the complexity of exploration in the large design space and to enhance cost-effectiveness, energy efficiency, and human-centric values. The toolset is demonstrated in a case study to retrofit a medium-sized building, where it is shown to propose a design that significantly lowers the overall investment cost while achieving user specifications.