Materials
100% cotton cord, a wooden ring, wooden beads (sometimes) and charity shop find or old furniture / wooden items being re-purposed. 
 
Currently, I have one Square One available and it used to be part of a draw. I left its knob on, as that is part of its history and is a cool feature.
 
Dimensions
Length when hanging is approx 45cm (top of shelf)
Shelf dimension are  22.5 cm x 22.5 cm
 
Variations
This is a one off piece, however, I can do similar shelves with wood slices or boards (rectangular in shape). Please contact me for requirements and I will let you know what I have available.
 
Important
Please use indoor pots without a drainage hole in it on your shelf.