Classtime; hey, welcome! We don't know where you're posting from, but if you were on the West Coast, or anywhere else it rains, or you have wet Winters, what Charles said about weather, in Spades!!!
If you see T&G exterior applications it's almost certainly something like Cedar. I love D. Fir, but not for the application you're talking about.
Having said that, if you enclosed the vertical applied boards in a 4 sided or maybe 3 sided frame, with the bottom open,, you might get away with it...but you'd need to reaaaaaly seal the wood! I mean Oil based; none of this Latex crap. It has to be WATERPROOF. It's still going to expand and contract, just not as much, so again, exactly what Charles said.