The person radical caps the character as a peaked roof, indexing 仓. Originally 倉 pictured a granary with a pointed top - a roof for storing grain. The 人 cap survives in the simplification as the visible roof-line above the storage space below.
The lower two-stroke shape pictures the door or opening of the granary beneath the roof. Stacked under the 人 cap, it completes the granary outline - a roofed enclosure with an entry - from which the meaning 'storehouse, granary' derives.
