Adam Clarke on Mark 2:4

They uncovered the roof - The houses in the east are generally made flat-roofed, that the inhabitants may have the benefit of taking the air on them; they are also furnished with battlements round about, Deu 22:8; Jdg 16:27; and 2Sam 11:2, to prevent persons from falling off; and have a trap door by which they descend into the house. This door, it appears, was too narrow to let down the sick man and his couch; so they uncovered the roof, removed a part of the tiles; and having broken it up, taken away the laths or timber, to which the tiles had been attached, they then had room to let down the afflicted man. See Luk 5:19, and on Mat 10:27 (note); Mat 24:17 (note).