A big thanks to FSMumford for drawing this in Sketchup. I had to re-draw it to take into account metric wood dimensions and bed sizes here in NZ, and also to remove a foot or so from the length.
We just gave it to my daughter today, and already I need to make some modifications. I immediately put some vertical grab rails at the top of the steps and slide. The steps are too big for a toddler (she's 3 today) and I didn't take into account how thick a pillow top mattress is! I really needed to make the end guards higher. In fact, were I to make it again, I'd probably make the towers taller and lower the height of the bed by 8-12 inches. While this would lower interior room, it might make the steps a more reasonable height for a littlie. If you're building for a 5 or 6 year old, this may not be an issue. Also, it would make the angle of the slide shallower (it's a bit steep, I reckon). I used 7 sheets of 16mm MDF but if I'd laid them out like FSMumford did in her plans I would have used less. Our (one car) garage is too small and the whole build process, including painting, was a royal pain in the bum. Fun, but a pain. Speaking of painting, next time (riiiiight) I'd try to paint as much as possible before assembling. I built mine in modules but even so it's hard to get a nice coat of paint on the insides of things. Edges of MDF need to be painted and sanded at least twice to look nice. Don't underestimate the time needed to get a good finish - I spent a third of my build time finishing (mostly, again, due to limited space). A narrow foam roller is great for cutting in but doesn't seem to get enough paint on to cover well on larger areas. In places I have three coats and can still see my pencil marks. I used Dulux Aquanamel.