This is the max I can do without looking too bad
It's 25 slots more than the diamond chest (1 column = 9 slots, 4 x 4 columns = 16 slots), in contrast, a single chest is 27 slots.
Does anyone has a better idea? (or perhaps a better design of GUI that would offer better storage)
that actually looks good to me cause you can use those slots for certain ores or put stuff there when collecting stuff to get ready to craft but dont have all the necessary materials yet