What is the meaning of "Yisfon"?
Rashi: It is covering with a roof.
Was the Bayis finished before it had a roof?
Radak: The verse means that first he built all the walls, and afterwards the roof. Gra - however, the roof was before the wall between the Kodesh and the Kodesh ha'Kodoshim.
What was the form of the roof?
Rashi: There were two roofs - one was for beauty below, and one of cedar beams above. 1
Kli Yakar citing Mahari: There were three covers on top of the roof.
Malbim: The Kesef Mishneh (Hilchos Beis ha'Bechirah 4:3) says that in Tugaramah (Turkey?), the nobles' houses have a roof of illustrated planks, and above is the primary roof. There is a gap in between, lest water leak from the roof. The bottom was called Gevim, for it was on Gav (on top of) the Bayis, or because it was illustrated (like the lower roof of nobles' houses - PF) and water would leak to there - "Asah ha'Nachal ha'Zeh Gevim Gevim" (Melachim II, 3:16).
What are "Gevim"?
Targum Yonasan: B'Hantuchin. Rashi - I do not what this is. I heard in the name of Menachem that they are nice, interwoven boards in a form. Shmei Korah (ceiling boards) is related to Shamayim.
Rashi: They are hollow bricks, like half-circle reeds 1 used to cover houses.
Radak #1: They are dug cavities, like "Asah ha'Nachal ha'Zeh Gevim" (Melachim II, 3:16). The beams were illustrated with cuts in the shape of cavities.
Radak #2: It is a dome (Gra - of stone); the roof was like a dome. It says {Pesachim 42a} 'three things are Govev height', i.e. bend it.
Radak #3: This is like Tzela'os, for the ribs of an animal are called Gav, e.g. 'Al Gabei Behemah' (Bava Metzi'a 2a). Also a person's ribs [are called Gav] when he is bent - "Al Gabi Charshu Chorshim" (Tehilim 129:3). "Gevim" is as if it says Tzal'os Beroshim, like it says below (verse 15) "b'Tzal'os Arazim b'Tzal'os Beroshim." The thin planks that are not wide like the others are called Tzal'os, for they are like ribs.
Kli Yakar citing Mahari: This is an expression of height, like "Harim Gavnunim" (Tehilim 68:17).
Presumably, this is like bamboo cut lengthwise in the middle. (PF)
What are "Sederos ba'Arazim"?
Rashi, Targum Yonasan: They are cedar planks arranged above the Gevim 1 for people to walk on, when they ascend to see Bedek (needs of) the Bayis. Yonason translates Sidra d'Richpas Reishei Shiryasa. Richpas is close together; the Targum of "Avei Shechakim" (Shmuel II, 22:12) is me'Richpas Ananim Kalilin. Radak - Shiryasa is beams. The Targum of "b'Tzel Korasi" (Bereishis 19:8) is bi'Tlal Sherusi.
Kli Yakar: Sederos is like Shidrah (a spine). The cedar beams were arranged like a slanted roof highest in the middle, just like the ribs come out from the spine on a slant.
Radak: The Gevim below were of Beroshim. It says in Divrei ha'Yamim II, 3:5 "v'Es ha'Bayis ha'Gadol Chipah Atzei Beroshim." It did not mention the top, for it was of cedar.