My husband built the shelving unit out of a plastic "egg crate" panel that we got at Home Depot. You can find it in with the florescent lighting supplies. It's all glued together with water proof epoxy.
We left about an inch air space on three sides. The plan was to fill that space in with orchid potting mix/bark chips so that the shelf wouldn't be seen at all.
Inside the shelf are a whole bunch of
ceramic beads used in hydroponics. They're inert, neutral ph and allow for air space AND also wick up moisture as needed by the plants. Plus they are super light weight. I DO want to be able to take this to work and put it on top of my horizontal filing cabinet.
On top of the shelving unit my husband tightly fitted a screen layer. . . when I say, tightly fitted, what I mean is that he folded
and ironed the window screen material to fit over the shelving like a glove. . .ur, a tailored bed skirt. What can I say? *snicker*
On top of that will be the orchid mix and all the fun stuff.