The present invention relates to a system and method for modelling the physical characteristics of a building. Models of buildings, such as floor plans, are often produced when renovation work or other work is planned. Manual measurements maybe taken (e.g. using a tape measure or an optical distance meter), and these measurements are subsequently used by a draftsman to construct a model of the measured space. This is time consuming. The present invention provides a system and method which includes a measurement and modelling process which assigns a unique identifier to openings that are shared by adjoining rooms when plotting measurements. These room associations are then used to determine the layout of the rooms within a building model. There is significantly less time and cost involved in generating a computer model of the measured space, using the present system and method.