The aim of the proposed work is to investigate the technical and economic suitability of a gas turbine combined heat and power system in commercial buildings. These systems are widely recognised as a promising technology to provide significant fuel savings and carbon emissions reduction where they have been widely used in industrial settings due to the relatively constant electrical and thermal loads required for industrial processes. However, their deployment has been relatively stagnant over the last few decades due to challenges such as poor planning and policy measures, energy market changes and regulatory barriers. In this context, a preliminary system design and optimisation procedure has been developed based on a sensitivity analysis of different scenarios of building loads, market and weather conditions. The optimisation is performed considering several technical and environmental parameters (e.g., energy and exergy efficiencies and primary energy saving), as well as economic indexes (e.g., net present value, pay-back period, profitability, etc.). This allows the suitability assessment of the investment for different market price scenarios under different heating degree days demand scenarios. The analysis is carried out using an Italian case study as it exhibits a wide range of heating degree days variability, while subject to a single pricing market. Results show that strong correlations occur between the technical and economic performance indices and the weather conditions for all considered configurations. The methodology and conclusions, if coupled with the possibility of applying clustering techniques to determine common patterns of energy consumptions in building blocks, represent a powerful toolset to carry out preliminary techno-economic assessment of a combined heat and power system.