The underground factory consisted of a number of tunnels laid out in a grid system. The main tunnels, numbered 1 to 4, were each wide and high. These were mainly used for access and movement of materials. Smaller cross-tunnels provided the main workshop and storage space. The total area occupied by the works was 53.34 acres. The tunnels had a floor area of , of which was not required by Rover and was used as an RAF stores area. There were also a number of surface buildings which included a boiler house, coal stores, electricity sub stations and a fire station.