Overall setting -- "loosely future Earth," say a hundred years from now, with plausible levels of realism (doesn't have to be perfect, but should feel familiar and match intuition). Climate change was not averted, sea levels rose, technology fell back somewhat (due to reductions in population, social upheaval, and so on) but the living memory of what was, still remains.
But this story takes place in Miami FL (or some other coastal city with similar characteristics). The median elevation of Miami, according to google, is about 6 feet -- so if we get 30 feet of sea level rise, the ground is underwater, but most of the taller buildings are still "dry," with only the bottom few floors submerged.
We'll handwave and say something was invented to treat the concrete in those buildings, so they're still standing, although everything in them was ruined. But I want to use these handwave credits as rarely as possible.
Now what I really want is for a small population of people to live in the upper floors of these skyscrapers, doing light aquaculture and basically just having a new and peaceful start, including the little society being stable enough to raise children. I think I understand how they can get fresh water (solar still) and keep out of the elements, but what I'm stuck on is the predators.
Pythons fill the Everglades and are just completely terrifying. I think I could believe that alligators can't climb stairs, but pythons can climb anything, swim for miles, and are just completely silent until they're, you know, eating your kids in their sleep. Not great!
So, uh, how do I keep pythons out in this situation? The "housing" is more or less open-to-the-breeze, since the windows and so on would be completely blown out decades ago, so I wouldn't think you could physically keep them out. I could hand-wave and say a snake repulsion system was invented, but it doesn't seem as plausible as "the concrete was hurricane-proofed and strengthened" and I'd rather come up with something more plausible, and preferably something that can be done in a straightforward manner by the people currently living there.
(I will say pythons is what I'm most worried about, and to a lesser extent other snakes, but there are plenty of other pests that could conceivably take up residence in these buildings and make them hard to inhabit for a peaceful human society)