You need:-

1) 2 planks (split in two) or 4 planks for legs Size 3 feet.

2) 4 planks for making shelves.

3) 2 hinges as per the legs width

4) Spare wood or planks again to make steps (I used four to make steps separated with 1 foot distance)

5) Screws, screw driver, Drill, Sander and paint.

Step 1: Make Legs for Ladder From Two/four Equal Size Pallet Planks

Now join legs by hinges and put steps per your desired distance\height

Step 2: Final Step

Once base with legs and steps is ready...put planks as shelves as shown in pics.

Note: I have put small wood piece under the shelves in a way that legs wont get slipped outside and inside.

Basically the small pieces are looking out the legs movement. (See pic 3 of this step)