This paper explores the method development of fire modelling in historic timber roof of Notre Dame Cathedral during the 2019 fire, using a combination of observational footage and multi-scale computational fire modelling. As a forensic engineering exercise, time-stamped images are analysed to reconstruct the fire progression. The study focuses on the choir region, particularly principal frames C07 and C08, where external footage provides the clearest view of the development of the fire. To support the analysis from the modelling point of view, computational fluid dynamics (CFD) simulations were conducted across multiple scales. Small-scale wood crib fires and large-scale compartment fire experiments were replicated using a two-plateau heat release rate (HRR) approach, capturing both flaming and glowing combustion phases characteristic of timber. These simulations form the basis for developing a scalable modelling strategy suited for real-fire in heritage structures. The insights gained are then used to propose a method development pathway for modelling large timber roof fires, such as that of Notre Dame. By linking the observed fire timeline with fire dynamics, the study demonstrates that publicly available visual data can serve as an indirect validation tool for fire-structure interaction analysis. The findings contribute to improving modelling strategies for real-world, large-scale timber fires in historic buildings.