I have a very small garden and most of it is in shade due to an apple tree.
The only place left to grow my veg, that gets any sun, is the patch of wall shown in the photograph.
I wanted to use window boxes in a stepped arrangement so that the higher ones would not cast a shadow on the lower ones.
I also wanted a structure that would take under an hour to build so that I did not lose heart halfway through.
Step 1: Feet.
I had two large beams at my disposal.
They did not need to be anywhere as thick as this but it's what I had.
I simply put them against the wall at my desired angle and marked the tops and bottoms parallel to the wall and floor.... and cut them with a bowsaw.
Step 2: Supports.
I just nailed on a couple of supports, making sure that the gaps were only slightly wider than the window boxes.
Step 3: Batons.
I nailed on some batons for the ends of the boxes to rest on.
Step 4: Bish Bosh.
Here it is, seeded with tomatoes and ready to grow.
I do not have another window box, so the fourth level will be a shelf with individual pots on it.
I figure that if I put a small circle of salt/sand around each foot, (maybe copper tape.), the slugs will go elsewhere.
If you make this and your boxes are not strong enough to be supported just from the ends then put a shelf across the batons and place the boxes/pots on that.
This summer I will be eating mainly tomatoes.