Ambrose of Milan

The cedar is suitable for hanging roofs, because this type of wood is tall and spacious, but not burdensome to the walls. The cypress is also suitable for ceilings and gables. Hence, the Church says in the Canticles: "The beams of our houses are made of cedar, our ceilings of cypress," explaining that the decorations of its structure are in these, as if the beams sustain the crown of the Church with their own strength and adorn its peak.

The Six Days of Creation ↗

Bede

The beams of our houses are of cedar, etc. Indeed, he calls his houses the various assemblies of the faithful throughout the world, from all of which the universal Church consists. However, the beams and ceilings designate the various orders of the faithful in these houses of the Church: for both are usually placed on high, but the beams are made for fortification, while the ceilings contribute more to the decor of the houses than to their fortification. …

Commentary on the Song of Songs ↗

Bernard of Clairvaux

"Our little bed is flowering, the beams of our houses are of cedar, our paneled ceilings are of cypress" (Song 1:16-17). She sings a wedding hymn, describing the couch and the chambers in beautiful speech. She invites the Bridegroom to rest. For this is better: to rest and to be with Christ. Yet it is necessary to go out to gain profits for the sake of those who are to be saved. …

Sermons on the Song of Songs, Sermon 46 ↗