I am working on a commission to build part of Birmingham Snow Hill as a 7mm scale diorama on three boards, which will model the full extent of the overall roof. At a later date it will probably be extended to complete the platform area.    For those not familiar with the station, this is what I have taken on...............     The biggest challenge has been working out exactly how it all fitted together, but happily it was all built with standard parts and dimensions. The crucial one was