By making a brush roof, do you just mean creating the geometry for angled roofs? If you're trying to angle brush faces you can use the vertex edit tool, which allows you to position individual vertices to where you want: here you could create a box, and raise one edge of the box.
But those are very simple roofs, aren't they? It's easy to make that kind of roof with the vertex tools only, just make two halves (make a box, then drag your desired edges upwards) and put them together afterwards, mirroring one of them. In fact, the roofs you're referring to might even be a bit thick - 4 or 8 units thickness is usually good.
Now, It's been a while since I've done any mapping, but aren't these kind of roofs practically "my first room" type of stuff? It's just transforming a flat brush surface into a sloped one.
Hopefully after going through these steps, it will open some doors for you to learn how to manipulate brushes.... CORRECTLY, not just sloping and stretching things.
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