Let him that is on the house-top ( ἐπὶ τοῦ δώματος) not go down, nor enter in, to take anything out of his house. The roofs of the houses were flat, with frequently a little "dome" ( δῶμα) in the center.
The people lived very much upon them; and the stairs were outside, so that a person wishing to enter the house must first descend by these outer stairs. The words, therefore, mean that he must flee suddenly, if he would save his life, even though he might lose his goods, he must escape, perhaps by crossing over the parapet of his own housetop, and so from house-top to house-top, until he could find a convenient point for flight into the hill country.