One of the reasons most PC cases are metal is for EMF protection, both incoming and outgoing. If you look in a laptop, the plastic parts usually have a thin metal cover on their inside faces. If you elect to do a case like this out of wood, you may see some unexplained undesired behavior.
I have also built an acrylic case but as far as wood goes you are not at risk of fire figure 3btu per watt. Worst that happens is the hot dry air dry’s out the wood and causes cracking but your pretty safe. I would suggest poly inside and out as dust clean up on would isnt that fun if it’s not sealed and you don’t want to have to use a damp rag to get it all off. So the poly coat you can wipe away dry and gives you a nice clean shine
You’d probably need to start with one of those older computer cases where the sides and top came off as one piece. All of my recent PC builds use cases where the top is permanently affixed to the chassis (though you could still skin it I guess.) Doing the chassis and case as all wood or acrylic, while very cool, would take a lot of tedious design work.