Storage Rooms:
Each storage room comes with 10 storage slots.
Each slot can store 1 "Unit" worth of Items, such as one purchase of shields (enough for a squad of 10) would take up 1 storage slot.
Materials take-up 1 slot per 20 "pieces" of the material.
If you ever go over your storage maximum, this excess is lost.
Each Unit of Food takes up 1 Storage Slot.
Gold is not stored.