屋上
おくじょう · okujou · JLPT N4 · noun
rooftop
🏢 屋上 = roof (屋) + on top (上): on top of the roof
屋 (oku) means house or roof, as in 屋根 (yane, roof). 上 (jou) means up or on top, as in 上手 (jouzu). Put together: the top of the building, the rooftop. Both use on-readings here: oku + jou.
屋 — corpse 尸 + reach/arrive 至
屋 originally depicted a place where one arrives (至) to rest under a roof, with 尸 here representing a covering or dwelling rather than a corpse. The character came to mean 'house' or 'room'. Today it commonly refers to a house or a room within a building.
上 — horizontal line above a baseline
上 is an indicative character (指事): a short stroke placed above a longer reference line shows the concept of 'above' or 'up'. The earliest oracle-bone forms used two horizontal lines for this; the modern shape added a vertical stroke for clarity. The core meaning of 'upper, above, to ascend' has stayed stable for millennia.