Peter, yes I could take the measure before assembling the paper model but in fact it require more work to understand where exactly are assembled the other parts. To my opinion it's better to assemble it and then cut it into several part according to the measure you need to take.
I've finished the plans and worked on cupolas, made of thin plywood plate (5mm thick - 13/64 inches) cut according to the plan and stacked with white glue and Araldite, to fix the metal bar at the center (in order to use the lathe).
Then come the work with the lathe to smooth the surface, I have now a wood cupolas base of the right shape for super details who will be added on it. There's 11 of them and none is the same, different shape and colors. This is the only time I'm using wood for this cathedral, all the other parts will be made of plexiglass or others materials. The wood was the right choice for an easy work on those onion shape, but heavy tool is needed.