I bought a loft bed bunk bed when my oldest was 3, bookshelf & drawers on one side, desk on the other. The bottom bunk slid in perpendicular to the top bed.
It became my youngest's when they moved out of their crib and oldest got my old queen.
It worked good - oldest dd liked sharing her queen with friends sleeping over, and when youngest ds had friends over it worked good for them to each have a bed.
We just sold it - ds is almost 15. He was getting to big to be comfortable in it, and it felt too cumbersome in his room (instead of cool like a fort).
If I did it again, I wouldn't bother with the desk side. He preferred a bigger stand alone more open desk a few years ago and then had both.
I think a loft bed that has a couch underneath (that folds out into a double bed) would be a good choice if I bought one for teens. It is pretty cool tlfor teens to have a couch in there room.
Now, both my kids have queens which they like. Dd will still sleep 3 kids in hers lol.