Factories are characterised by a long life cycle and substantial investment costs. In particular, factory planning and reorganisation lead to capital-intensive investments and have a significant influence on the liquidity of companies. Reliable data are the basic prerequisite for a valid economic assessment of intended factory planning projects. However, especially in early planning phases, the available data are often uncertain and inaccurate. This problem significantly impedes the early and precise dimensioning of operating resources, production areas and employees as well as their cost calculation for planned factories. This also increases the risk of erroneous cost-benefit estimates and potential misinvestments. As a result, an early economic assessment and cost estimate for planned factories is essential. Until now, a holistic approach that can quickly and precisely determine investment costs of different planning variants in an early factory planning phase with only limited and uncertain information is not yet available. In order to close this research gap, a holistic approach for calculating investment costs in an early stage of factory planning is in development within the framework of "ELIAS", a collaborate research project of the Institute of Production Systems and Logistics at Leibniz University Hannover and the GREAN GmbH. The central objective of this research project is the software-based development of an investment cost calculator in order to carry out an economic efficiency assessment for potential factory planning projects at an early stage. This article provides both a brief summary of the need and innovative capability of the research idea and the structured procedure for creating a planning tool that closes the research gap described above. By this means, companies are supported in making future-proof decisions at an early stage despite uncertain and inaccurate data.