Geographic Information Systems (GIS) can effectively support Urban Building Energy Modelling (UBEM) approaches, which are increasingly implemented and adopted to assess the energy performance of the existing built environment. GIS data may provide a suitable input base to perform building energy analysis at an urban scale. In this context, this manuscript first analyses geospatial open data both quantitatively and qualitatively, as they may supply useful input data sets to enable UBEM-based simulations. Moreover, this contribution also proposes a methodological workflow to effectively cross-check and pre-process geospatial open data, by also providing a GIS tool specifically implemented through the QGIS (Quantum GIS) graphical model designer. The proposed tool allows a user to automatically pre-process georeferenced open data and generate a suitable input file for UBEM simulations inside QGIS environment. It is also worth specifying that the herein advanced method is conceived to provide the georeferenced input data set required to perform UBEM simulations through the open-source EUReCA tool, freely released by the BETALAB research group of the University of Padova (Padova, Italy). The presented methodological workflow is a preliminary outcome of the ongoing research conducted withing the scope of the NEST (Network for Energy Sustainable Technologies) Task 8.4.7 project concerning “Urban Building Energy Modelling (UBEM) and urban green infrastructures modelling for Renewable Energy Communities (REC) and Positive Energy Districts (PED)”, financed by the European Union -NextGenerationEU- and coordinated by the University of Padova. At the end of the paper, the main findings and results derived from the application of the proposed tool to a case study area in Cagliari (Italy) are discussed to point out strengths and weaknesses of the method, by also bringing to light some relevant gaps affecting open geospatial data sets.