Take all those measurements and decide how big your bed will be and how high you'll raise it.
Sketch out a plan - we used SketchUp, but drawing on a napkin would work just as well. Basically you want a flat bottom, two risers on either side and a top. While you might be tempted to skip the bottom, it adds structural stability and prevents the whole thing from sliding around. A flat plywood bottom is also preferable to 2x4 bracing as it makes it much easier to slide the storage bins in and out.
Things to consider:
size of the bed (we fit a double mattress with room on all sides)
how you will fit in the storage bins (we made sure the openings were wide enough to utilize the most space possible)
best use of lumber - you'll want to minimize the number of cuts and scrap