I built a loft bed from scratch. Thanks, Home Depot.
It had to hold a queen size mattress, and not fall apart. From that criteria, I was able to piece something together in my head that actually went together in real life. I had no way to cut the materials effectively at home, so I had to get it all done by the friendly staff at Home Depot.
I only made one mistake, which was corrected by cutting notches out of the beams on the ends of the bed so that they would fit properly into the metal hangers. I was amazed at how it came out, but I think the secret was not allowing myself to do any of the cutting.
I put night lights on the stairs which are triggered from a motion detector switch that came from my old house. So the stairs light up gently when you go up or down them.