Recover -Recover is used over roost for fear of a smart opponent playing something like an Earthquake when he has lost his flying typing. Restores heatlh and softens up the rest of regenerator when injured by stealth rock. I guess you could use roost if you didn't want to get X4 damage from stone edge, but I think earthquakes are a bigger threat for him if he were to lose his flying typing.
Sacred Fire-STAB fire, breaks through most everything that doesn't resist it, and sets in a bunch of burns on the opponent.
Brave Bird-Deals with Kyogre, Palkia, Reshiram, and all those other annoying guys.
Substitute/ Tailwind/ Whirlwind/Earthquake-Tailwind allows him to get past his base 90 speed issue, which can really screw you over in ubers. Earthquake offers another combat move, and is generally pretty handy, especially against things like Palkia, which double resist him, or Zekrom, who can be OHKO'd on the switch with the help of hazards. Whirlwind can allow for phazing, which is an option to pair with Substitute if you want to sacrifice a second move, and substitute allows Ho-oh to PP stall low moves like water spout on Kyogre. Be wary of thunder though. You could combine it with pressure and run it out pretty quickly, but I think his new ability will be of more use.
Suggested item: Leftovers
Suggested Nature: Adamant
Suggested ability: Regenerator