Well, everyone else has made a suggestion so here's mine. You could have a crown roof.
Google it for pics, but basically it means you can have the same tiles and pitch as the main house until the height limit is reached, then flat roof to wall.
The other one I was thinking of is the parapet roofing, I reckon you could easily lose 0.5 metre by having a wider parapet, the drawing link is not correct for you but will give you some idea
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