So I'm in the process of making the new accommodation block for our new house mates - Mr & Mrs Call Duck

(thanks goes to [member=3983]Brucklay[/member] for providing them in a couple of weeks).
Just wondering what products, if any, do people use to protect the wood of their poultry housing (providing its made of wood that is)?
The roof will have shed feelt on it, and I would like to paint/stain/protect the underside of the house block from moisture coming upwards from the ground or indeed rain splash.
Its only the outside facings that will be getting painted/treated and not the inside.
Thoughts, comments, experiences please are all welcome.