I have only visited Brooklands once since I left in 1971 and I lost my bearings completely so my next project was to try to model the location of the main works. I have a document showing the internal layout of the building and it says that the total area was 703,363 ft^2 .
Having traced the drawing and done the required maths I think that the front of the factory, at the erection shop end was 138 metres wide. That seems a big big to me. The length front to back is 372 metres and the width at the "DO" end is 227 metres.