Thanks.  I went back and forth on several different options for the inside.  I wanted to do cedar but that was to expensive and the reviews online for what I was going to buy said most of the planks were warped and couldn't be used.  I looked at paneling and didn't find anything I liked.  I decided to go with birch plywood until I went to a different lumber store.  I found 1/4" underlayment that looked very similar to the birch plywood but was less than half the cost.  I'm going to stain it after I get it all installed.  I think the wood grain will show more with the stain and sealer on it.  
Pappy, you are right.  I doubt this will ever be 100% finished.