Worldguard Help

I am making a new prison server but I have ran into a problem. I have a tree farm where a player can go to get wood to sell but I don't want the users to be able to build or destroy I only want them to be able to destroy the birch wood and the leaves and that's it. Would I also have to change something to allow them to pick up the saplings and wood?

Thanks,
Arcticcat340