Make it from 25 x 25mm planed timber and sheets of 6mm ply.
Make frame of the 25 x 25 glue the ply to one side or both sides.....your choice. on the back corners of the carcas fit triangular corner pieces to stablize the frame. Don't forget when making up the frame/carcas to allow for 25 x 25mm shelf supports. All parts can be doweled together so buy a dowel jig it's easier.
If interested how I'll send a drawing if you post your email address in this section....use the answer to YOUR question form.
BB
December 2009