Loft bed over bench seats?

You could start with the Classic Bunk Beds http://ana-white.com/2010/09/classic-bunk-beds-cleverly-designed.html and just change the design of the front section.

Note that if you build it to be disassembled, the front section will be flimsy since there is only one board connecting the corners. I would make the bench frame as separate pieces, you could make them similar to the way the legs attach to this table top http://ana-white.com/2010/04/plans-simple-outdoor-dining-table.html but using 1x3s.