The body for my brake van owes something to Mark's model, but also a lot to a Model Earth 7/8th scale design we featured in Garden Rail a few months ago.
I've decided the ends will be "metal" and main body "wood". In reality, it's all various bit of plastic I've got kicking around.
There are no drawings, I just cut stuff to fit the guard figure who has been sitting on my shelf for a couple of years. The curved top owes it's design to a tin of varnish that was handy for drawing around.
Inside, the main beams are from some sawn strip I bought from a model boat show thinking it would come in useful. It has, but I've got loads more, well, it was cheap and I'm sure we all have materials like this...