Great start Paul.  Sketchup is perfect for getting a feel for things before setting to work.  If you switch to 2D view, you can then print these out once you have them to scale, I used that method for Oswestry Works to get a full size mock up with the prints stuck to foam board.  It was a quick and easy way to get a feel for the size of the diorama, what constraints there were on getting the camera inside the building etc.

One note - those blue faces, that means they are inside out, not a problem for what you are doing here but should you want to 3D print something, the faces need to be reversed (right click on face, click Reverse Face).

Thanks, Alan, for the tip. i agree with you about getting the feel for the model, particularly as most of the structures are now a distant memory. There is a lot of detail to be added from the old newsreels, but once in SketchUp the plan is there for the future.