Interesting idea, but didn't really come together

I really liked the idea of this book - four very different people meet on a roof top where they've all gone to commit suicide, end up talking to each other, and forming a group. The book follows what happens next - do they all make it or do one or more of them return to the roof to finish what they started?
The problem, for me, was that it never really went anywhere.
I felt like the book did a lot of aimless wandering. I did like that there was no neat ending tied up with a bow. Overall, it wasn't bad, but it wasn't great either.