With the walls a little clearer more of the structure is revealed. Unfortunately it appears that the slab was poured after construction. The corrugated iron is thus below the slab line and in connection with the ground.
Not surprisingly this has led to rust and in parts disintegration to point there are visible holes. I haven't yet dug down deep enough to know the thickness of the slab or what foundation the wooden frame is in. (Hopefully it's not just hardwood sitting in dirt.)
I suspect that I will have to trim at least 300mm of iron off the bottom and replace it. Along with this I will plan to extend the slab around the edges as a path with drainage. Unfortunately this all costs time and money. (Should be a bit of fun though).
As part of the clean up I've ripped out most of the shelves the previous owner had used. There was certainly a variety of materials (hardwood, softwood, honeycomb core, MDF, and far too much chip board) and fixtures (random screws, rivets and lots of nails.) He was certainly fond of nails.