Smart homes for ambient assisted living (SHAAL) can provide cognitive assistance and telemonitoring to foster independent living at home. However, building a personalized SHAAL is a complex and time-consuming co-construction process involving IT specialists, healthcare specialists, caregivers, and the elderly person herself. Not surprisingly, it is very difficult to access and integrate all these expertise at the same time in the same place. That is why we are developing a do-it-yourself (DIY) approach aiming at enabling a non-expert to build her own SHAAL. To get there, four phases need to be supported: design, installation, tests, operation, and maintenance. This paper focusses on the design phase. It presents an innovative prototype platform that leverages Augmented Reality (AR) and Artificial Intelligence (AI) to guide a non-expert through a user-friendly “do-it-yourself” (DIY) process to design in situ a SHAAL. This platform captures each category of expertise using templates and models. Thanks to ontologies and case-based reasoning, AR makes available this expertise and assists a user while she is designing in-situ her SHAAL. Two preliminary experiments involving expert and non-expert users showed promising results.