Can anyone tell me if Particle Board would be durable for a one tier cake? I am making a turntable for a grooms cake and need something durable and big enough to hold the turntable style cake (ie: length and what not). Thanks!

I'd use plywood. Particle board warps when it gets wet or with too much moisture.

Is plywood durable enough for a 3 tier cake? I'm making my first 3 tier cake this weekend and not sure what I should put it on. Also, how do you cover it?

Just the fact that it's plywood or particle board isn't enough. It's the thickness of the wood that helps.
Plywood is *very!* sturdy. Particle board can be if thick enough and well covered. One way to cover them is w/plastic tableclothes. I used staples to hold the tablecloth on. That's not a problem because the staples are on the underneath side of the board so won't interfere w/serving. And usually I used a staple gun rather than a standard, office type stapler. They are thicker and hold better.

I use MDF a lot for my cake boards. I buy a 4 x 8 sheet and my husband (or me if he is gone) cuts whatever size I need. That way I can make it whatever size or shape I want. It lasts a very long time and is cheap. The last time I needed some I had to go to my local lumber yard and they were out. I purchased some sort of plywood or particle board (yes, I know the difference). It's worked just as well. I always get 5/8 inch thick.I cover them usually in one of two ways: I wrap paper over it with plastic over the top then glue it with a glue stick on the bottom. No glue on top. The other thing I do is cover it with fondant. Either way it gets ribbon around the edge. Since it's 5/8 inch thick I usually find lots of ribbon to coordinate with the cake color/design.