To give a bare back garden a focal point, create an outdoor lounge area with basic gravel. A simple white sunsail over head pulls everything together. A painted tree stump in a white lacquer creates a unique textural table. >> pretty space for summer!
Now, a shelf like this, covering a wall from floor to ceiling would be pretty clever in a small flat. Tons of storage and room for fancy stuff, but you could also place furniture (like a sofa) in front of it if you want to.