roofs are a similar problem - having realised that rooms have ceilings even though you can't see them in aerial view, I can get my head round that. creating sloping roofs is not so obvious so I hope this will happen in a later version!
I did look at the tutorial which says to use "plan > edit room points" but I don't see that option in the plan menu. Ah well I only just downloaded and started to play, maybe doing the octagonal house as a first project was ambitious