For stairwells, typically you should place an AP near the stairwell or at least measure if it would penetrate from outside the stairwell. Some stairwells have material that make it difficult to get RF through. You also might not be able to drill a hole into the stairwell to run an ethernet cable for an AP, so your options are limited. Downtilt antennas are still limited by their obstrunctions; but the majority of the campus APs that Aruba makes today. have built-in downtilt antennas, so in most cases anywhere you can mount a campus AP, you will have downtilt coverage. Again, do a test in the area to see how much mileage you would get.
With regards to elevators, most people don't even attempt due to the cost; and those are very well-capitalized organizations. If you search for elevator on this forum, you will be able to see how painful it is and what others have done.