The 176 m free-spanning dramatic roof structure of Heathrow's Terminal 5 main terminal building will undoubtedly become one of London's iconic buildings. This paper describes the various processes that the roof team used to ensure compliance and system integrity in order to guarantee that the 17 000 t structure could be built safely while negotiating one of the project's critical paths. The paper describes the engineering issues and how collaborative working contributed to achieving one of BAA's most successful sub-projects. The focus of the paper concentrates on the structure and describes how the design criteria set the fundamental requirements for the construction operations while the design of both permanent and temporary works was developed together. It details the rigorous review and approval processes and describes why risk assessment and compliance audit were crucial. The importance of the team structure and how this operated in conjunction with the lifting protocol to guarantee the success of critical operations is emphasised. It covers the development of the engineering procedure and how this was used to develop the hold points to control key stages. A full description of the construction engineering studies is provided to highlight the complexity and extent of preparation undertaken.