Shading is a frequent problem in attic rooms. Of course, it can be easily solved with a roll-up blind, a window film or a venetian blind, but if a classic style curtain is desired in this room also, the case is not easy at all.
The solution in the case of windows on sloped roof is putting on two curtain rods. The upper one has the same function as on a normal window. The lower has the role of holding the fabric of the curtain. The lower has to be placed under the window. Both of them should overhang the two sides of the window, just like in other rooms. In the case of a floor length curtain, the fabric simply should be put behind the lower rod. When it is pushed, the rod will hold the fabric on the sloped roof anyhow. However, in the case of a short curtain, the lower rod has to be put in the fabric, just like the upper one. One or two sided curtains can be made in both cases. Of course, the curtain can be attached to the rod in any ordinary way (rings, fabric flaps, keeper etc.).
In the case of a full width window on a vertical wall, the problem might be the lack of space above the window for the curtain rod, because of the joint of the sloped roof. It is harder if the window itself is not rectangular but follows the line of the roof. It is worth to ask for help of a professional curtain company for a beautiful work. The length of the curtain has to follow the line of the window. Two rods will be needed in this case also, but the fixing is not a free choice because of the skew, since the rings would slip off by the gravitation, for example.
If the window on the vertical part is too small, or not symmetrical in its place, a more spectacular curtain solution can improve the sight. The feeling of a bigger window can be reached by a fabric complementing the furnishing of the room and covering the whole wall, this way the detrimental wall-part can be turned to a focal point. Curtain tassels and wall hooks will be useful.
Ask for help of an interior designer for solving the curtaining of attics.