We had a structure constructed in our allotment car park. It is about 18" - 2' square and abut 4-5 high on 4 legs which were sunk into the ground. It has 2? 3? shelves, the lowest one being perhaps 2' - 2.5' off the ground, and walls around 3 sides from the lowest shelf to the roof, which is corrugated (I think) material that slopes downwards towards the back. The rest is made out of wood.
The empty shelf areas can be filled each year with bamboo or other similar prunings.