People use different methods for getting their roofs rights (see FAQ: How can I create a roof on top of a house?). A few models are available, or you can create your own - often by combining different basic shapes.
The blog post How to design a sloping ceiling with a window is full of useful hints and a step by step guide to one kind of ceiling/roof. You can also use the Shape Generator Plugin, see thread,6600. Hansmex' guide from 2011 has detailed instructions for creating roofs. In thread,6372#27608 you will find a couple of other approaches described, including links to some generic roofs in SF 3D models 330.
Good luck.
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