Do you think is possible to suggest a plugin to generate mansards, by imagining how it would work? I mean, from someone who never has written a line of code (me), but could help imagining how the computer should build it.

I suspect that at some point this type of roof will be integrated in the Roof Generator plugin.

You still need to create the gutters. You can take a look at my DodecagonRaingutters library but they are not the same as in your image of the house. It does give you an idea on how to create Lego parts for your specific gutters (my rain gutters are also "Lego parts").