It costs 2 hoppers + 1 observer + 1 dropper + 1 copper golem + 1 chest for every 3 double chests.
The red line shows the path of an unsorted item(the chest facing us is the one in the positive x and z direction).
This is usefull for storing a lot of different items before you have a massive amount of iron.(right after first entering the nether)
This lay-out was chosen for being aesthetic and being fairly compact.
by RevealAcademic804