Hello everyone, my first post!
 

I now have planning for my extension and am starting to think about the external insulation. New extension is shown in grey. The area in yellow is currently pebble dash and the new part will be block. I'm going to insulation the front of the new part so it flows right across smoothly. However when should I look to insulate and render the pink area? (Same both sides). Would this be before the attic trusses are put up and screwed into the wall? Or after and before I put the tiles on?

I would say, after the trusses are up. Heavy structural work done and any fixings to the original building are not going to damage your new insulation.

Then all the insulation can be done in one operation, and cut in to suit.

The corner from pin to yellow will need some attention.

 

Very helpful drawing btw.

Thanks I'll go for that! @saveasteading