Objectively, it's not very important at all, it's just an offhand reference in the U.A. To be clear, most people interpret it as referring to a concealed storey between the penthouse and the roof, not literally just the flat roof. The feeling is that this helps to rationalise why there would be a secret passage leading from the Baudelaire mansion to an otherwise random location, and why it should be so important to protect the penthouse floor.
But it wasn't through the penthouse... it was just at the top of the stairs. Theoretically, anyone with access to the building could walk up there. Although I guess if you didn't live up there, you really wouldn't have a reason to go up there. But yes about what Dante said, it's not just the roof, there is a secret story before the roof, I think.
Faith is being sure about what we hope for, being convinced about things we do not see. Hebrews 11:1 For God so loved the world that he gave his only-begotten Son, that whoever believes in him shall not perish, but have eternal life. John 3:16