The hubs and I built this for our two year old daughter. It was pretty straightforward, and wasn't a huge time commitment. We had taken her out of her crib a few months back, but she had been sleeping in a twin mattress on the floor, so she could get used to not being in a crib. She was so excited for her new bed.
Note: we used rockler brackets to attach the rails to the headboard and footboard, so its not just one huge piece, and when we move we can take it apart. They worked Great!!
Also, because she is two, and we wanted to keep her lower to the floor, we decided not to use a box spring for now, so we took 9 inches off the bottom of thr headboard 4x4s. this ensured there was not a gap between the top of the mattress and bottom of the headboard. If we choose to use a box spring mattress later, it will still work out fine and look great.