Read the Roof with dormers tutorial .
Could be something like this:
You could start from something like this:
Hint:
It's not perfect but, with some imagination and a lot of work could be acceptable.
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A computer program does what you tell it to do, not what you want it to do. Murphy's Law
When all else fails, read the instructions. Murphy's Law
If you don't like "AS IS", DIY. Dorin's law
