The description of the aicraft's geometry represents one of the critical aspects of conceptual design and is, of course, fundamental for the tool here presented. The main result of the first sizing of a new aircraft is simply a 2D sketch, not particularly useful for more sophisticated aerodynamic analysis for which a 3D representation is required. The ability to address the geometry information from the beginning using techniques able to communicate with CAD and CFD-preprocessor tools widely available in the industry is now a necessity. In this respect, a specific module developed during the SimSAC project is AcBuilder (Aircraft Builder) that has been adopted as the standard Pre-Processor for NeoCASS. It manages a set of geometrical parameters that are general enough to ensure that a wide array of aircraft morphologies can be represented and analyzed. Based upon this geometrical description, the structural and aerodynamic modules access the appropriate parameters that are required for the specific method at hand (beam/plate models, aerodynamic panel methods) and create their own numerical model. As result, AcBuilder generates an XML file used as input by NeoCASS.