A slanted ceiling adds character to a room but it can make decorating difficult. If a window sits between two sloped walls, you might be struggling with how to cover the window. Below are some ideas on how to deal with these challenges.
Just as is the case with any window treatments, first you must recognize what the purpose of the window coverings will be. Do you need privacy and light blockage or a solely decorative element? How do the slanted ceilings fit in with the task? Are they something you want to accentuate or hide?
If the window covering is decorative and the window sits between two slopes, you can accentuate the slants by placing gorgeous fabric where the wall meets the ceiling from the tip/peak and down. The fabric can be gathered into itself using ribbon or binding so that it doesn't block the window.
If you need to cover the window for privacy and light blockage, then a simple roman shade hung inside-mount will suffice and won't interfere with sloped walls.
As A Room Divider
If there is no window but you want to hide the slope because it is one-sided in the room, consider hanging fabric along the wall and using the space behind for storage. This can make the room appear more traditional by treating the fabric wall as the fourth wall of the room. Have clothing racks behind the curtain to serve as an extra closet or build in shelving for extra storage. Read below on three options for hanging the fabric.
Use a sliding track such as the type of curtain tracks found in hospital rooms. It's easy to find a sliding curtain track system online or at your local hardware store. Place the track on the sloped wall or where that wall meets the ceiling. Attach the curtains to the track curtain clips. In a room like this, you will most likely want to make your own curtains to get the size right. Find your favorite fabric at the store and hem the edges.
Another option is to use a steel piping system. Place a long custom-cut steel pipe from one end of the room to the other end to serve as a curtain rod. You'll need to purchase the steel pipe and flanges. The flanges will be hung on the walls adjacent to the one you're covering.
A third option is to sew buttonholes in the top of the fabric and place them in hooks that have been inserted in the slanted ceiling.