I have interesting question to add to yo

I have interesting question to add to your bag of tricks from my lates interview for SSAS skills. How you design cubes for ad-hoc reporting? It was related to discussion on chaging requirements and often hidden questions that users do not articulate ahead of time. Knowing that best practice is not to design generic cubes. There is no such thing cause the cube answers specific busines questions to help to define business strategies. However, the users wants flexibility in analytics and asking more and more for open-ended sort of design inclusive of dosens of dimensions with hierarchical complexity over 2 bln rows facts or more. What do you think, do we know now with 2008 or 2012 versions the best practice to optimize the design of such monsters?