To make your own flower stand with PVC pipe, purchase with a 4-way fitting. It conforms to φ20 PVC pipe, and placing it in the four corners makes it easy to make a strong cube. If you want to increase the strength, add a side by adding a four-way joint at the middle of each side.
With a commercially available flower stand, I make my own because there is not the height and size I am looking for, but the PVC pipes are ideal for stands because they are easier to cut and cut thanks to strength and there is no worry of corrosion.
Eight cubes are required per cube, but Monotaro is saved because it can be bought cheaper than the home center.