When we built the basement, we needed to run a set of external stairs up to ground level.   Rather than have these awkwardly appear in the garden, we built a 3x4 m box around them with the plan to put IBCs in the bottom for rainwater harvesting and to run a deck over the top and create a mezzanine level deck. it is west facing so should be a shaded sun spot in the evening.   All the roof rainwater is currently piped through this area in 110mm pipe on its way to a soakaway.