The book (or series) I'm looking for is set in a post apocalyptic world where a giant wall around the entire world separates the Northern 1/3rd from the Southern 1/3rd. I'm pretty sure the southern 1/3rd was completely barren wasteland and the top was lush greens. I just remember the book cover had like a wall with a turret on it. The main characters were either teenage friends or siblings tired of living in squalor/poor barren part of the world.

There was something about kids practicing in an arcade to drive these flying cars/fighters to get pastthe wall. I think the rich people lived more towards the clouds or even in space.

I know this is vague, but I'm hoping someone can help me out. I used to read a lot more and am wanting to start reading more again. For some reason, young adult novels just seem to be what I prefer because reading is a leisure activity for me and YA novels are easy to read and have good stories I like.