Totally depends on where you are, and it actually does become a legal thing. Some places it is not legal to cross all willy nilly (CA) and some places it is (NY) New Yorkers are coordinated adults who watch for traffic and cross whenever they want (love it, always loved it being there the most). They hurry so they don't hold up cars. Cars yield within reason but honk if the person walking is being a jerk about parading like it's a big "event". In Los Angeles you have to act like a toddler, walk a block out of your way to where you're "allowed to cross", stand awkwardly in the beaming sunlight while the speeding traffic gawks at the spectacle of an actual "pedestrian" and "wait for the walk signal" or literally, a cop may arrest you for jaywalking. C'mon! Annoying!
Personally, I'm the type who likes to hurry across the street whenever I want if it's not impeding any cars, and when I'm driving, I yield when people are crossing and I give the "go ahead" wave. I'm not a hothead, so I don't honk even if they're being slow pokes.
SO. In the parking structure you described. I would probably defer to law if there was one. I'd stick the crosswalks and be proper if I was with my toddlers, but I'd just go across however I wanted on my own without holding up any cars if there was no big legal warning posted about jaywalking.