This verse is very similar in form to the Marcan parallel (13.15), except that Matthew has smoothed out the grammar, as he frequently does. The situation reflected is that of the Palestinian house with its flat roof, which was generally accessible by a stairway from the outside of the house. One must not leave the impression that the man is up there repairing the roof of his house. Translators may say “A person who happens to be on the roof of his house should not take the time to go down and take his possessions from his house.”

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .