I am planning on getting "wood crates" to be the legs of a lofted bed.
Each box measures 18" x 12". For thickness, the long sides are strips of 1/4" pine and the short sides are solid 3/4" pine:
I want to make the legs 54" (18*3) tall in front, and stacking four crates with some 2x4s at the top (to fill in the gap to reach 54".
Starting in the bottom left corner and going clockwise: I plan on cutting out slots for two 2x4s in the crates for stability. Then, along the back left, there is a 1' 2x4 for support (and will probably add another one in the middle). Along the back bottom is a 1x2. Inside the front bottom is a 2' 1x2. Last, the top frame is made of 2x4s.
Will this design be strong enough to support a sheet of plywood under a mattress? Is there a good rule of thumb related to figure this out?
Edit
The wood crates are pine and they are all the same dimensions. They are fastened together with staples as seen in the picture. (These are commonly available at home improvement stores.) My qualm is how these are marketed as decorative boxes.