With the country’s expanding population comes the need for more homes to accommodate its residents. In the Netherlands, there is a growing housing shortage. Fast construction techniques of prefabricated dwellings erected on existing flat roof tops may be a solution for saving land and resources in and around urban areas. Flexible solutions with sustainable design techniques that cater to the masses are essential for the Circular economy. The research topic is presented, and the research questions are framed in terms of technique and relevance to the construction sector. Flexibility issues with contemporary house designs are highlighted in the literature review, and circular building concepts are discussed in order to develop design requirements for building components. The many types of prefabrication are identified, and a system is chosen for the design concept. Building physics strategies relating to steel’s thermal and acoustic qualities are examined, and these strategies are noted for prospective integration into the design. A design suggestion for modular housing top-up units is presented. Different options for internal partition walls and façade architectural components are presented, all of which are modular and designed to extend the life of the components through reuse. The modular components are used in a top-up situation to validate the architectural quality of the design. The design criteria given out in the research are used to evaluate the building components. Finally, conclusions are drawn and research questions are addressed.