Hi AHarper,
I did this very quickly with what you gave us with the original logline...
In a post-apocalyptic future where the poor live underground, a teen sets off on a perilous journey to the affluent city above, in search of life-saving supplies.
INTENTION: to get life-saving supplies. (figured might as well make it more intense.)
OBSTACLE: perilous journey/everything on that journey.
I'd probably push in on the obstacle. How can we make this worse for him? How can we make it harder?
I'd probably put more in like the teen's wounded/dying father needs the supplies (this way it's more primal) but it's quite a lot to digest already.
Good luck with your writing!