Dear Engineer,
Thank you for your inquiry.
We recommend that you export 3D models from AutoCAD as obj files so that the textures are preserved and also exported. For models in *.obj format, a *.mtl file and a *.jpeg file must be located in the same folder. Visual material properties (e.g. reflection, transparency, specular highlights, etc.) are defined in a separate material file with the file extension *.mtl (Material Template Library), whilst texture data is stored in separate texture files (e.g. *.jpeg files).
An attic cannot be created on most imported 3D models, but only on the roofs of standard buildings. We agree that the error message ("An attic can only be created on building roofs with an inclination smaller than 20°.") is incorrect and unhelpful. We have forwarded this to our development department for correction.
Instead of an attic, you have the option of inserting fireproof walls:
It is correct that the software does not automatically detect mounting surfaces. You import a 3D model as the building envelope and must manually define where mounting surfaces are located. Please also refer to our FAQs: What should I consider when importing 3D models?