1.40 is okay for a teenager, I had that too. 1.20 also works if the room can't fit more. Loft bed - yes, we have one right now - annoying, never again. So the kid got it because I always wanted one when I was younger and never got it. Now I know why. Making the bed on that thing is really hell (because everything around is secured with beams and netting and cushions, I can't reach anything, the morning waking up is also great when she’s lying in the farthest corner and I can’t even grab a leg to pull - but she sleeps restlessly and I’m afraid she might slip out otherwise). Uh, on the topic
Double sockets in every corner, where the desk will eventually go a few more, considering PC / laptop or whatever. One network socket too. (the WLAN and network factions always argue about that).
And yes, furnish according to the age, now the floor space for toys really counts.
(I’m looking forward to the time when all that stuff finally gets thrown out...)