We just relocated into a refinished attic space that is quite large---except for height. At about 6'4" high at the center, the ceilings drop dramatically to about 3'6" on each side. It is a big, open, space, otherwise, with no closet and no nooks. So, we built a closet!
We installed a closet rod at the front part of the room (the rear made more sense, but that is where all of the windows and skylights are.) and put up a curtain to mask it. We got two extra curtain panels, one to use as a "door" to the room, and one to pin up along the side of our closet to close it off completely. We chose a light, airy white to keep the room bright and open. Our curtains are pretty long for the space, but we kind of like the fabric pooling up on the floor. That, and we're not sure exactly how long we'll be living here--if it turns out to be more than a few months, we'll be hemming them. If we were staying longer, we would probably have a piece of plywood cut to fit the side "wall" of the closet, and either paint it white or upholster it with our curtain fabric. But, for now, this is good.
Since the ceiling is at a pretty severe angle, we didn't mount the braces traditionally, at a 90 degree angle. But with some extra screws they are pretty secure how they are. We used three braces four our 5 foot rod, and since one end of the closet was against the wall, we used a cup brace for the end. This idea could easily be translated, though, to virtually any area that you have room for a closet. We managed to install it on a ceiling at a 45 degree angle.
We were worried about our DIY closet having too much of an added on, out-of-place, college feel to it, but we were quite happy with the results. Now, we have plenty of closet space and a clean look when the curtains are closed.