First treat this as a geometry problem to build a box sized exactly to cover your space, you will need sides and a bottom:

First:

• Measure all the sides carefully, and the bottom carefully.
• Get a compass and measure all angles carefully, since it is a slant and all angles will probably vary from one another.
• Bring measurements to your local lumberyard, and a schematic diagram with measurements included on it.
• Cut redwood or cedar planks to the dimensions and angles you have measured.
• Be sure to include a wood floor to the sides, or all the dirt will fall out.
• If the slope is too high to keep the dirt in, get some zinc chicken coop wire and put that on top of the soil like a metal hair net, to keep it in place. You can plant seeds or seedlings or plants inside by either clipping the wire where needed, or keeping it in place and interplanting wherever a hole may be located.
• Buy enough redwood or cedar to build a box using your measurements.
• Use non-rusting nails or better yet, screws.
• Allow for a little drainage on the bottom part of the box, and
• Have a plan so you are prepared to re-use the water that comes out of it (if possible on your property), rather than have it go into the rivers/ocean.

Step 2: Get enough dirt/potting soil by calculating volume based on the information on the package of the soil.

Step 3: Arrange plants based on their water-needs, so that the top plants require the least amount of water -- succulents -- ? (dato che l'acqua drenerà verso il basso e le piante in basso riceveranno la maggior quantità d'acqua).

Step 4: Fertilizzare più frequentemente di quanto si farebbe altrimenti, dato che l'acqua perderà rapidamente i nutrienti del terreno, dato che è in pendenza.