Major landscaping, especially in a trapped space, needs careful planning of the logistics for preparation and build. It is magnified when access is restricted.

Careful surveying of levels and right angles are essential, especially when viewed from above. Your eye is incredibly accurate and able to spot defects when you have so many parallel lines.

Choice of suitable quality materials can be a saving in the long run as they look and feel much better and are likely to last a lot longer, standing the test of time and weather. They usually have the added advantage of being more accurate to build.

When importing topsoil, the best quality you can find is essential as this will significantly affect the choice of planting you have in mind. I would always choose a gritty loam for raised container beds as good drainage (preferred by most plants) is difficult to correct in heavier soils.

A mid-range ph in the soil will suit most planting. The addition of lime, or acidic based mulches, can help you adjust this if you want plants like heather, which need acid conditions or lavenders. These grow readily in mid to alkaline soil types.