I've been testing Classic MixNite, and Roost is nowhere near useful on this set. Mainly because it's way better off just throwing out strong hits after another rather than spending a turn to activate MultiScale, which would easily be broken due to sand, LO recoil. On a Dragonite with 0 defensive investment, it's taking huge chunks from the opponent, and add that with LO recoil it's not getting back to full health after 1 turn of Roost (in which case Dragonite's dead meat).
I definitely found Tailwind and ExtremeSpeed MUCH more useful, since they both circumvent Dragonite's terrible Speed. Tailwind is nice since it can use its powerful special and physical moves rather than ExtremeSpeed to kill faster opponents, but ExtremeSpeed's emergency priority has also come in handy.
Earthquake was also certainly useful when facing Rain teams with Jirachi and / or Tentacruel, which can use Dragonite as set-up fodder. I'd say Tailwind or ExtremeSpeed has more overall utility, though.
Basically remove Roost and slash Tailwind / ExtremeSpeed (whatever order). Earthquake may be good enough for that 3rd slash. But yea, Roost isn't good on this set - the turn you spend Roosting is better off spent dishing hard hits or setting up Tailwind.