The Automating Concrete Construction (ACORN) project explored digital workflows from the design to the construction of reinforced concrete building floor elements, reducing carbon emissions and increasing efficiency of building processes. The resulting digital tool, named SQUIRREL, enabled the design of shells, composed of prefabricated segments, through an interactive framework, composed of parametric design tools, and informed by architectural, structural, and construction requirements, including building integration, fabrication, transport, assembly, and resource reuse. This paper presents the design and implementation of the SQUIRREL tool, focusing on the main design tasks for a segmented reinforced concrete shell, including formfinding and segmentation layout definition. This paper also documents the development and application of a Design Space Visualisation module within SQUIRREL, which streamlined parametric studies used to inform the design decisions behind the modelling and implementation process. Finally, we discuss the right balance between design automation and user interaction, which should inform the development of future construction-aware computational design tools.