Has anyone ever done this? Cedar bookcase turned into raised bed

I picked up a large, old, bashed up cedar timber bookcase. No wood chip here - proper cedar. I knocked the backboard off and laid it on the mulch in the garden. I put garden rocks in the base for drainage. I am planning to use it to plant ornamental. Not vegetable as I don't know what might leach out of the stained timber and into the soil and thus in the edibles. So ornamental only. The depth is about 30 inches which should be deep enough to plants some flowers and maybe grow from see. Anyone used a book case frame before to make a raised garden bed and if so, how long before it fell apart? Thanks.