The rules (at least the german ones) seem to indicate that you move the tower first, and then negotiate the action of the space the tower is in now.
You negotiate for the move and the building action. In the event that the active player cannot successfully conclude a negotiation, she may choose to move the tower into a building, at which point she must either take the action or can be forced to sell it for minimum cost (any amount of money or objects offered).
But suppose the tower starts in a building, can you first negotitate the action of that building before starting to move the tower?
You *must* first negotiate the action of that building, or take the action for yourself.
Edit - in both cases above, if no player wants to take the action of the building, it may be passed.