The following paragraph by M. J. Selman in the New Bible Dictionary, 3rd ed., provides a good summary about houses in Bible times.
Many houses had two storeys, though, since no building in ancient Israel has yet been preserved with a complete roofed ground floor or ceiling, the original height of a building is not always certain. Upper rooms were reached by stairs or ladders. These rooms provided the main living and sleeping accommodation (cf. 2 Ki. 9:13, 17), and guests could also be looked after there (1 Ki. 17:19; 2 Ki. 4:10-11).
Roofs were constructed from beams covered with branches and a thick layer of mud plaster, though the rafters were sometimes supported by a row of pillars along the middle of the room. Cylindrical stone rollers about 60 cm. [23.6 inches] long were used to keep the roofs flat and waterproof, though roofs needed to be re-plastered annually prior to the rainy season to seal cracks which had developed during the summer heat.
The family would often sleep on the roof in summer or use it to dry raisins, figs, flax, etc., in the sun. A parapet was to be built as a safety precaution according to Dt. 22:8. Vaulted roofs were certainly in use in Palestine by the Persian period, while the tiled roof also appeared before NT times. The rooftop was also a place of worship, either for Baal and especially the host of heaven (Je. 19:13; Zp. 1:5), or for the true God (Acts 10:9).
The first photo shows a portion of a roof made from wood and mud. You will also notice a roof roller on the roof. After the winter rains it was necessary to roll the roof.
The next photo shows the roof a little later in the year after grass has grown on the roof and died under the summer heat.
From the inside of the house the ceiling might look something like this.
Notice the New Testament texts implying such a roof.
When they were not able to bring him in because of the crowd, they removed the roof above Jesus. Then, after tearing it out, they lowered the stretcher the paralytic was lying on. (Mark 2:4 NET)
The account of Luke, a gentile physician, adds an interesting point that creates a small problem in interpretation.
But since they found no way to carry him in because of the crowd, they went up on the roof and let him down on the stretcher through the roof tiles right in front of Jesus. (Luke 5:19 NET)
Did you notice the reference to roof tiles? One of the Translator’s Notes in the NET Bible discusses this problem.
There is a translational problem at this point in the text. The term Luke uses is keramos. It can in certain contexts mean “clay,” but usually this is in reference to pottery (see BDAG 540 s.v. 1). The most natural definition in this instance is “roof tile” (used in the translation above). However, tiles were generally not found in Galilee. Recent archaeological research has suggested that this house, which would have probably been typical for the area, could not have supported “a second story, nor could the original roof have been masonry; no doubt it was made from beams and branches of trees covered with a mixture of earth and straw” (J. F. Strange and H. Shanks, “Has the House Where Jesus Stayed in Capernaum Been Found?” BAR 8, no. 6 [Nov/Dec 1982]: 34). Luke may simply have spoken of building materials that would be familiar to his readers.
There are other possible interpretations, but I hope this information with the photos will help you better understand the biblical text.