Hi there, all,
At last, I've got some illustrated progress to share.
I've been held back by wet weather, short days, walking man's best friend, writing Christmas cards and waiting in for a gas cooker repair man.
The gas cooker fault was electrical and serious - no oven = no Christmas turkey!
Happily, the second repair visit took place today (ETA between 10:31 and 12:31, where does their computer get these times?) and seems to have fixed the problem.
Here is a photo of the roof when work started this morning:

You can see the frame with the nearest cells loaded with Kingspan. (The light reflected from the Kingspan foil covering seems to have given the camera a problem - I had a go at the pictures with MicroSoft Photo Editor but couldn't achieve any improvement.) At the far end, you can just see the corners of the tarpaulin, I left the ropes on that end attached in case sudden rain required me to replace the tarpaulin. You can also see the length of flashing along the lower edge of the roof and the two roof sheets that I managed to fit last Saturday; the second sheet only had a minimum number of fixings at this stage. The far sheet is concealing the length of flashing fitted to the far end. On the near end of the roof you can see the crawler boards I used once I decided to work from the top rather than over each side off the top of a ladder.
On the high edge of the roof, you can see a board temporarily nailed to the edge of the frame. The function of that board is to provide a stop against which each roof sheet is to be pushed to keep them in line. That didn't work out quite as I'd hoped. Where the sheets overlap, I've applied a bead of butyl sealing strip to the upper surface of the underneath box - once the upper sheet touches that sealing strip it's grabbed and further movement is impossible. You need to have it in position before they touch!
So, both before and after today's cooker repair call, I was able to get some work done. Today's activity comprised completing the fixing of sheet #2 and fitting sheets #3 and #4. I've been fitting the fixing screws along the inner purlins first. Then I fitted the foam polythene eaves filler between the roof sheets and the flashing along the lower edge followed by the lowest row of fixing screws. I was able to do those working off the step-ladder - didn't need the gooseberry kneelers!
The fixing screws are described as 'self drilling' but I've found it necessary to centre pop and drill a small pilot hole, especially where the screw has to go through both roof sheet AND flashing. They come with a pre-fitted metal washer and synthetic rubber sealing washer.
The light was going and it started to rain just as I was fixing the last few screws this afternoon (sunset at 15:57) so I wasn't able to get a photo of all the roof sheets in position. Still, I packed up feeling quite chuffed at our progress and left the tarpaulin where you see it in the photo.

I'll try for a photo at the start of the next session.
My lovely but shy assistant played a key role in today's (and every day's) activities, helping carry the roof sheets and passing up to me various tools that I'd left at ground level but discovered I needed once I'd climbed up onto the roof.
The next work package is to drill the fixing holes along the top edge of the roof sheets, remove the board, fit the eaves filler and then fit the screws. Then the flashing along the top edge fits on top of the roof sheets with its own gap filler and is screwed to the edge of the frame and the top of the roof sheet boxes.
The flashing along the lower edge need some more screws to attach it to the frame and the older roof fascia and I'll need to check that the rain does get from the edge of the roof sheets safely into the gutter - it now has 4" further to fall and might need some guidance!
I also need to contrive some form of flashing for the near end of the roof. I didn't buy enough from the roof sheet supplier but I think carriage on just one 3 metre length of flashing might make it unaffordable. We'll press on with the other jobs and see what the old grey cells throw up.