Done the latter, going to do the former today, having trimmed up the foam.
When it comes to fitting the plasterboards, I read the suggestion that I should fit them with the longer side across the rafters, but given the shape of the roof, I can get more efficient use out of very expensive material by doing them the same way. At the top, I wasn't even going to attempt to put in full-sized sheets, as they are too heavy to be manageable at that height, but was going to cut them into halves, anyway (so the two sides would be the same length). Does it matter/make any difference? I'll tape and fill the joins before the boards are skimmed.
