We just built a 32 sq' raised bed - the highest part off the ground is about 4', the lowest is about 2' (it's on a slight grade). The boxes are 16" high, but there's only about 10-12" of fill in there. We also have a 16 sq' raised bed at ground level - same height and filled the same way. Here's what we used (all approx, based on my rapidly faltering memory): 1 yard of half mushroom compost and half leaf compost; 3 cf' compressed peat (actually 6 cu' when fluffed out); 2/3 of a 4 cu' bag of vermiculite and 4 50lb bags of a compost that was made of kelp, chicken manure and something else I can't remember.
The kids claim it stinks, but it doesn't bother me. Then again, I love the smell of manure and hay in a horse barn so don't go by me! But you can just tell from the way it looks that it's way better than my soil would have been.
One thing I'll tell you...we used a double layer of small holed chicken wire on the bottom, with a layer of weed barrier on top of that. We had to add several wood supports (on top of cinder blocks at all corners and a few middle bracing points - it's a T shaped box) to hold up all that dirt when we wet it down. Be ready for that.