After much checking and reading by fellow proof reader I seem to have got part of the instructions for the Aircon unit the wrong way around in the photos
P12a 2.5mm Basswood Aircon unit should have the Kerfing lines FACING the roof when glued and the thinner 0.8mm plywood part P12 should have its Kerfing lines facing upwards to wards you, which is opposite to the picture in the instructions. Doing it this way will keep the edges inline with the sides as each piece follows the radius of the roof. Smooth on smooth.
The next batch has the part! I have a system when packing which is a parts list with drawings which is foolproof, but it looks like it's not idiot proof yet!