Pics of the insulation and internal sheathing going in:
As I said before, Celotex is marvellous stuff. Measure, slice with a stanley knife and then snap along the cut.
I've used 30mm thick boards in the walls, stood off from the exterior boarding by approx 15mm by some galvanised staples hammed into the uprights at regular intervals. Allows for an air gap between the exterior boards. Then it's just friction fit between the uprights, and any joins between boards done with aluminium foil.
I'm covering the walls in 9mm OSB boards - just screwed to the uprights. I'm doing the gable ends first so I can run the OSB up to the upper 'rafter' and screw it on there as well - then I'll insulate the roof with 25mm celotex (there's not as much room up there for any thicker plus an air gap), and then board over it as well.