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I used a Cardboard with density ≈ 300 g / m²
1- 4 pieces of Cardboard with size: 150 cm x 15 cm each (Rails).
2- 8 pieces of Cardboard with size: 37.5 cm x 24 cm each (Rungs).
3- 4 pieces of Cardboard with size: 20 cm x 15 cm each (Footpads).
4- 2 pieces of Cardboard with size: 7 cm x 8 cm each (Hinges).
5- 4 pieces of Cardboard with size: 6 cm x 15 cm (Top pads).
6- 16 pieces of Cardboard rolled with 7 cm long and 8 mm Ø diameter (Pins).
2- On the Rails each 30 cm long drill a 8 mm Ø hole, 2.5 cm away of edge on both sides of the U shape Rail.
8- Make a 8 mm hole 1.5 cm away from the edge of each Rung and in the middle of both sides (let the over lapped side be in the bottom).
9- Trim 1.5 cm x 5 cm from the edges of the top side of each Rung (this to enable the move of Rung inside the Rail).
10- Cut exactly the middle of each Rung only 3 sides and leave the forth side to work as hinge.
11- Although the width of Rungs and Rails are same (5 cm) still you can insert Rungs into Rails, insert Pin to holes of Rung and Rail (leave 1 cm on each end of the pin, make 4 cuts along this 1 cm of pin, bend the cuts and glue it to Rail (make sure the none cut side of the Rung facing Bottom).
12- Repeat step 12 for all Rungs.