I don't pretend to be an architect or architectural engineer. I'm not a structural engineer or roofing consultant. That being said, the materials used in any roof design would definitely include the weather, extereme or not, in the building. Those materials would be made for use in Las vegas temperature environments. Expansion and contraction of the materials used in construction are included in structural design of any building. Ever hear of expansion joints?
What proof do you have to support your statement about Phoenix and Tucson having a problem with leaky roofs? I lived in the Phoenix metro area for 32 years. The only time there were leaking roofs it was due to poor construction, if new, and poor maintenance if older. Wood, if properly maintained, shouldn't absorb water at all. A roof that is properly maintained shouldn't allow water buildup to the point of collapse. When drainage is blocked and water is allowed to pool past the structural weight limit, what do you think is going to happen?
How many of the older casinos blueprints do you have access to? How do you know that their roofs have crappy drainage systems?
This isn't a personal attack on you, just a rebuttal of the reply to PJ's question.
PJ there are either design flaws in the leaking casinos or the materials used were wrong or improperly applied. Maybe both. There really is no excuse for there to be leaking like that.