A quick note on elevator door keys - different elevator manufacturers use different keys. They are uniquely shaped and not interchangeable. I know this only because in my line of work, I have to access the inside of elevator shafts all the time and work inside them.

And if a modern elevator does have a hatch in the roof of the car, it will likely be locked from the outside. I wouldn't say it'd be impossible to open from the inside, but it might be tough.

That's an awesome site, and there's a lot of good ideas there.