I need a 30 x 18 inch board and I can't find a ready made one in that size. I went to Home Depot and bought a 3/8 inch thick plywood and had them cut it to size. So what do I do next? Do I cover the wood board with foil paper then cover with fondant or can I just cover with fondant directly. What would be the best glue to use to adhere the fondant directly to the wood? I would appreciate your expert opinions. I have never had to use bare plywood for cake board before.

If you want your plywood returned to use again, I'd cover it with poly-foil and a layer of clear contact paper, or white contact paper. This will make it easy to wash clean for repurposing. (of course, your cake won't touch the surface of non-foodsafe materials because you'll use a cardboard under the cake.)

To help fondant to stick to your covered plywood board, you can spread piping gel on it first.

Put a sticker or something on the bottom of the board with your contact info and saying to return the board if you want it back. I'm surprised how often people throw away perfectly good wood.