I built this for my kids 20 years ago. Its made with very light weight steel studs. I realize that I undersized the floor joists, one split and it it sagging.
I have 3 choices, leave it, which is a liability when I sell the house (not a good option), tear it down, possibility of a few $100, or jack it up about $100.
I'm thinking of sinking some concrete piers below it and getting some pipe and house screw jacks to lift it up. I went inside it and overall its pretty solid.