Having looked at some more images it looks like the ends of the roof look to be moulded fibreglass or something similar. You’d be surprised how few pictures there are of roofs of coaches although this site was a good source.
More filler was used to create the raised roof ends which were then sanded back, which seemed to take forever.
I also glued in the doors, roof vents and buffer beams that came from Floyd Kraemer on eBay. The roof vents were fitted by first marking out using a combination of the original layout on the Big Big Train coaches and images of ready to run 00 gauge coaches.
Some plasticard steps below the doors were also glued on.
I’ll cover the making of the chassis it’s sitting on shortly.