Raised Garden Plans Raised Garden Bed Question? ?

Raised Garden Bed question? ? - raised garden plans

I 6ftx6ft only room in my house with a garden in an empty concrete slab of about. My question is: What should I have taken in my bed, to allow for clearance in a concrete slab to? I thought of putting two pieces of plywood, rose slightly angled so that the flow is minimal, but I am so hard on the termites and the rapid deterioration of wood in the floor care. All other proposals for the drainage in the raised bed in particular?