Where to put a design wall?

In the next few months, I'm going to be moving into my fiancé's house--which means that I get to redesign a sewing/craft/office room from scratch. I'm super-excited, and have been scoping out storage options at IKEA and reading up on organization ideas in a neat book I bought. The only problem is that it's a long, narrow room, and both the long sides have a sloped roof, which limits my wall storage space and will make it difficult to hang a design wall:

It used to be his "junk room." You can see he is still working on moving the junk. :)

We thought about maybe putting in a partial room divider flush with the closet next to the door--but that won't give me any space to step back from the wall, which is the whole point of it.

Does anyone have any suggestions, about the design wall specifially, or how to deal with sloped walls in general? I'm thinking of painting the top part with magnetic paint, if I can find it, to at least allow me to use that space to some degree.