propane water heater venting

Currently putting on low-profile barrel tile roof on "weathered in" addition, so considering options for venting the future water heater. I'm leaning towards a wall vent vs. a roof vent to avoid another roof penetration and potential flashing problems with the tile. Intuitively I think I would prefer to have a non-powered unit. Had the propane co. tech (who does their plumbing work) out, but he wasn't real familiar with through the wall venting. Have googled a bit & looked at the non-powered unit on the Bradford-White site. Plan to talk to my local plumbing supply and try to find a local familiar with wall vented units, but sure would appreciate some opinions before I get to the part of the roof where I would have to put the vent if that option turns out to be better for some reason.

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