Actually a re-check of my calcs, I made it 108.65 as an area based exercise.
However, I stick to my 122 estimate: I did this assuming that you'd still have to buy full length cladding boards for the triangular area and cut them later (i.e. you can't order cut boards you have to order full lengths, and I read Milli's question about what you'd need to order not what you'd need to use).
If I allow for the triangular (treat it as a square and half it, cheat I know), then i do get the 108.65 number that is close to Zarf and Claws
