Mark 13:15
In those days they generally had a flat roof that could be reached by a flight of stairs from the outside. So, it would be easy to exit from the housetop without entering the house.
One might ask how this would apply if a person happened to not have such a housetop setup? And the answer is that this is not to be taken to mean that all would, but it is (like the rest of these coming verses) meant to encourage swiftness. To escape from the impending destruction quickly is the point of the passage.
Heavenly Father, it is a great comfort to know that you know the end from the beginning. Even though we do not have that knowledge, you have shared so much with us. Thank you for your wisdom. I will praise you for your loving kindness is amazing! In the name of the Lord Jesus Christ I pray and praise you, Amen.