I, too, love beadboard - the tongue and grove kind, not the kind that comes on a pre-formed sheet and is really paper. If I never again see a shiplap wall, I will feel blessed. SO overdone and rarely done well.
What you do need to realize is that finding beadboard that is clear and has NO knots, will be difficult and very expensive. And if it has ANY knots at all, it must have multiple coats of BINS (a shellac-based primer) put on it prior to painting it. If it doesn't, the knots will bleed through and make stains. With new wood, even with BINS, you may have the occasional pop-thorough of the sap in a knot.
I made this mistake on my sun room ceiling about a year ago. I had no idea the wood would not be clean and knot-free. Well, now I had nearly $500 worth of beadboard boards, which had been painted and which the sap was coming through rapidly! I should have made the contractor just "eat" this, but instead had him do multiple coats of BINS and then paint. I still have 2-3 spots on the ceiling that have come through over the past year.
So, when it was time to do the ceiling of my front porch, I bought Azek PVC beadboard and then had it painted. It looks very, very good, will need rot, and no problem with sap and knots. I would highly recommend using this for your porch roof.
Beadboard on an interior ceiling is often used in summer cottages from the early 1900's. It was left unpainted and also totally covered the walls. It was maintenance free in unheated summer houses where moisture would have caused paint to peel. It would cost a fortune to do today in clear wood. And it would look like a Michigan summer cottage.
Q
like this look with the trim
Q