Sloped ceilings add so much charm and character to a home. We recently took our attic room sloped ceilings that looked like this - The entire knee wall is actually hidden doors - so the area behind is completely accessible. We use the space for storing Christmas decorations, heirloom gifts that we can't part with but don't necessarily use daily, and of course, the kids use the space for hide and seek. This was a fairly easy project - but time consuming since the walls are each sixteen feet long - that my husband and I tackled over the course of a few days, working a few hours each day on it. We decided on making the wall 48" tall, because this is where the ceiling height becomes useuable for furniture, and it also helps maximize materials use.
The easier way to do this is to just build a pony wall 48" tall x the length of your room, and install it plumb and level. Then trim out the top and bottom to give space for the full overlay doors. We love how this project turned out and know it will greatly improve the function and look of the room.
Video Tutorial of Building this Knee Wall with Doors