I've built them not too long ago and I'd like to share. I'm presenting the steps with the 'after' photos since I didn't document it at the time.
1. 4 Electric clamps (those small black ones, actually the color doesn't matter)
5. X-Acto knife
Step 1: Setup
2. Holes in shelves: Drill using a 4mm wood drill two holes on the opposite side (the side farthest from the wall), 2-3 cm from both edges.
3. Make 4 rope clamps: Take the electric clamps and CAREFULLY cut the plastic from them. I held them with the pliers (you can use a vise) and cut them with an X-Acto knife. What we're looking for is the metal part inside them and the screws.
It's easier to remove the plastic when the screws are removed (but don't throw them away!).
4. Cut rope: Cut the steel rope to the desired length + enough excess for mistakes in measurements. Make a small loop on one side of each rope piece and fasten it very tightly with the wire rope clamps (not the ones we made),
Step 2: Mounting the Shelves
2. Stick the plastic screw anchors in the holes. I used a hammer, but any blunt object is usable.
4. Hang the rope's loop on the anchoring screws with the washers. Screw the screws as much as you can, till they touch the wall.
5. Screw the top shelf in place. Pass the rope through it's front hole and lock it with the prepared rope clamps using the flat head screwdriver. Make sure the rope clamps are as tight as they can be !
6. Repeat step 5 with the second shelf.
7. Cut any excess rope.