The building sector worldwide is responsible for massive CO2 emissions. These emissions stem from both existing and newly constructed buildings, particularly from the extraction and production of materials. Solutions include promoting circular construction, smart investments, and political measures. However, information on materials, quantities, and routes is often incomplete or inaccessible. The “Colouring Dresden” project aims to gather, explore, and communicate knowledge about buildings via the open platform “Colouring Dresden”, part of the international Colouring Cities Research Programme (CCRP). It is Germany’s first citizen science project focused on data collection and disclosure about the built environment, especially buildings. In collaboration with stakeholders, the project developed research questions, adapted the platform, prioritized data collection features, and established citizen science actions and communication channels for knowledge transfer. These actions and knowledge transfer were crucial to the project’s success. Various evaluation methods assessed their suitability in citizen science, providing insights into participant motivation, interests, and benefits for science, society, and individuals. The evaluation revealed significant differences in response quantity and data quality during data collection. The results demonstrate that citizen science projects can be effective in the built environment context, offering insights into appropriate action formats and evaluation methods. This contributes to the advancement of citizen science in Germany, enabling targeted planning of future urban citizen science projects to enhance participant motivation and collect information to reduce CO2 emissions in the building sector.