1 - When creating a roof, the workaround used most often is creating a section of wall, than export, import and rotate it.
The top and bottom ends of the wall become the left and right side of the roof.
Using the function Top colour in 3D view it is possible to give the top a different colour. After importing the model, it is possible to adapt the colours using Materials -> Modify.

In the list of Model materials, the top of the wall is shown with its correct colour/texture.
Unfortunately the material for the bottom of the wall is missing. Is it possible to add this?
Would it also be possible to add the other two sides of the imported wall section to the material list?

Thanks you

Hans