i.e. can you demolish a ruin without a floor?
This one I would say definitely. While I think a breath action on a ruin is more effective... some people can't control their gusts of wind so well, and would rather drop and try to jostle them out to the neighborhood.
i.e. can you use the power "Climb" on a ruin without a floor?
This one I wonder about. I guess because it says you can put your monster on a building... that you can't put it on a ruin.
Building does not equal ruin? Once you have a ruin, there is no longer a building... so... No
Erm... one problem with this logic... The Demolish action says: "If your Monster’s Paws token is touching the Sidewalk surrounding a Building, you can attempt to demolish that Building."
So the big question then... is a ruin still a building?
If it IS, then you can do both... if it's not, then you can't do either.