The roof now has battons (that's the smaller pieces of wood that go across the joists I think) and some kind of waterproof sheeting (it's called Balaroid Breather, and it's a roof tile underlay - I'm enjoying the jargon. Builders love jargon just as much as software engineers!). Well, it's certainly waterproof, as tested by this afternoon's showers!
And the spacing for 2 of the veluxes (2 more to come!).
Our roof is coming in tomorrow, weather permitting. It probably won't be completely finished in a day, according to David, but hopefully the rain will hold off long enough.
Here is a detail picture of the extra bits of support under the joists. I'm sure they have a name! I'll have to check it out.