Breather box construction?

[super vw]

Hey guys, im looking at making myself a breather box. not sure if i will need it but it wouldent be bad to have so i want to make a custom box for my firewall (i dont want to use the dinky little crap ones they sell for 20 bucks in the mags)

So the questions are:

-What materials (have a MIG welder only, so mild steel, but that thickness is best?)
-How much volume would be best?
-Do i need to incoperate baffles to seperate oil/air?, would plates with holes in them be sufficent?
-Should i use barb fittings or would a reusable fitting be best? (more expensive with a aircraft style fitting, but worth it?)
-Finish? do i need to coat the inside as i would have to use mild steel to prevent rust? but with what?

Thanks!
Jonathan