jhb171, your comments are welcome, full of ideas and offer realistic options. I think if jhb171senior was on the platform carrying out inspections I would have to consider the permanent way foreman, Paddy McGartland standing at his hut on the convent siding pulling on a cigarette and telling his men to 'keep busy'!
The shed measures 10x6 outside with a sound 3" frame clad with T&G boards so I guess I lose about 6" all round. I will be filling the studwork with quilted insulation and sheeting inside with 'smartply'. The roof is PVC coated tin on a plywood pitched and trussed roof. I will insulate the inside of the roof with Kingspan foil backed insulation boards.
The floor is solid ply on 4" joists and on top of that I'm adding insulated exterior grade ply. Our directors office is having a refit so I've been promised carpet tiles from that.
I'd love a continuous circuit but something tells me space would dictate a U-shape, as you have already suggested.
Thanks again for your thoughts.