This study focuses on the problem of how to structure spatial and component based building data with the intention to use it in the simulation and analysis of the performance of buildings. Special attention was paid to the interoperability and optimization of the resulting data files.The study builds its investigation onto XML (Extensible Markup Language) data modelling framework.The authors have studied different ways of arranging building information in XML format for effective data storage and have developed a data modelling framework called bmXML for buildings. Initial results are two-fold: a VBA application was developed to create the appropriate building model in AutoCAD with the intention to write building data in bmXML format, and a JAVA application to view the file thus created.This paper primarily focuses on the former, i.e. the AutoCAD application and the bmXML format.