When you build a new house, you shall make a parapet for your roof, so that you do not bring bloodguilt on your house if anyone should fall from it. – Deuteronomy 22:8
Homes in Biblical times (and often still today) had flat roofs which afforded the advantage of additional outdoor living space. This mitzvah, to erect a protective fence around one’s (flat) roof, ensured that no one would accidentally fall off while enjoying the cool evening air. “If you build…” The law is the same if one buys, inherits, or is given a house as a gift. Why does the Torah use only the verb to “build”? According to the rabbis, this is meant to teach that always one must be engaged in “building,” that is, developing the human community – building and planting for ourselves and for coming generations.
Rabbi Mitch Levine