A collapsed roof sets the scene: a building, probably an old one, has given way and left its inside open to the sky. The comparison that follows is striking. The roof has fallen "like a borrowed hope," as if hope were something lent to us that was always going to be taken back, or that never quite held up once we leaned on it.
Then the poem turns to an owl, which seems to understand the silence of the ruin better than any person could. The speaker doesn't claim that knowledge for themselves. They defer to the bird.
The last lines move from loss toward possibility. A "naked bed" could be a bare garden plot, or something more private, and the question is what to let grow there. The mood is quiet and sober, but not hopeless. Losing the shelter, and the false comfort of borrowed hope, seems to leave a kind of freedom, which fits the title's "radical openness."