Explanation:

- Option 1: leading

- This is the correct choice. "Leading up to the roof" makes sense as it describes a staircase that takes you to the roof, indicating direction or connection.

- Option 2: leaving

- This implies going away from something, not suitable in the context of describing a staircase's function.

- Option 3: looking

- Not appropriate here as it doesn't convey the idea of a staircase taking you to the roof.

- Option 4: lasting

- This word implies duration or endurance, unrelated to a staircase's direction or connection.