tower world

in a world where everyone lives in one giant tower seperated in multiple classes poor, middle, business, and rich the people living in poor have to buy oxygen just to breathe to go up you must climb a 5,000 steps stairs to an elevator but every once in a while it stops at another set of stairs for another area in your class you cannot go up the stairs without a certain price so there are guards to make sure one climbs up without paying you live in the poor class wooden houses and some are just collapsed the price to go up? 50,000 price for 12 hours of oxygen? 150 choose what you are guard or civilian if you pick guard you choose your rank(recruit, experienced guard, squad leader, sergeant, enforcement officer, commander,)