Here are 2 great ideas. One is using piping, and the second one is using crown molding.
Opal...A simple fix is to buy one and put in the closet but I love the vinyl covered metal ones that you add the brackets to the wall and then attach the shelves or baskets where you want.
We've done closets a few different ways
I wasn't happy with an inexpensive set, even though it looked okay, it just wasn't very sturdy. The more expensive Rubbermaid set I redid my closet with was adjustable, sturdy and attractive. My husband redid his with wood shelves, clothes rods on two walls, but without the flexibility of mine. So some of it is budget, DIY ability, and how you want it to look.
You could put pieces of wood on the wall then rest shelf on then to hold it up