Parameter based design explorations inevitably require a unified master model that represents the current design state, where each parameter being explored is essentially a critical sub-case of this master model. Throughout the constantly changing design state, it is beneficial to maintain a master model that is flexible and adaptive. This paper describes the design process of a complex building whose master model documented the design logic through implementation of software code. This process is illustrated by the case study of Lotte Super Tower (Seoul, Korea) from the beginning of schematic design to end of construction document phase. By maintaining the master model as a platform-free software code, in contrast to platform-dependent methods, the case study illuminates the advantages of documenting the generative logic behind design variations in a way that allows greater flexibility and a higher level of alignment with design intent.