Some of these ideas are fantastic
I recently put up five, deep shelves into my built-in wardrobe. My bedroom isn't huge, but I use it for crafty things as well, so I really needed more space.
My friend suggested that maybe I just wasn't making the most of the space I had.
So now I have three crates on the floor of my wardrobe for fabric, etc (and my sewing machine), the next two are for clothes and bags, the middle one is for books/paints/clutter/works in progress, and the final two are substantially smaller so I use the first one for shoes and the second for plain storage. That means whatever doesn't fit anywhere else.
It's working perfectly though, and the best thing is that I can just shut the door if it ever gets messy.
I'm not a very organised person but I find that shelves really help me to keep things apart.