Altaria can resist Fire and Grass Moves, so it's going to be a big help against Sun Teams, just that you will have to be aware of Gliscor with Rock Slide or Conkeldurr with the possible Ice Punch (which could also be Rock Slide), Altaria should somewhat do better in a Sand Storm, just give it a Charti Berry to help it take Rock Moves better while something like Conkeldurr can either kill Excadrill or just bring it down to it's Sash and kill non-Chople Berry T-Tar with Drain Punch, kill Landorus with Ice Punch.
At the end of the day, Altaria will need help to handle Sand, but will be really effective in the Sun.
Item: Charti Berry
Nature: Bold/Impish/Relaxed (Relaxed for Trickroom)
Ability: Cloud Nine
EV's: 252 HP, 96 Def, 160 Sp. Def
Dragon Pulse/Draco Meteor/Dragon Claw
This Set will let Altaria take 2 Hits of Rock Slide from Adamant Tyranitar, did some calcs on this, Dragon Pulse/Claw and Draco Meteor are there for stab, if you plan to run a Physical Set, run Dragon Claw, if your running a special set, you can choose either Dragon Pulse or Draco Meteor, Draco Meteor lacks some Accuacy, but has more power than Dragon Pulse.
Heat Wave can deal some damage to those that resist Dragon, Pluck can let Altaria take advantage of the opponent's held berry.
Dragon Dance raised Altaria's Attack and Speed by 1 stage, Tailwind can help your team outspeed faster Pokemon, Safeguard can prevent Burns, Poison, Paralysis, Confusion, Sleep, etc.
Protect to scout what your opponent will do, Substitute to take advantage of Altaria's Resistances. Be careful of Ice Types Attacks, so watch out for the likes of Metagross, Conkeldurr and Mamoswine, if somebody can test this out and tell me how it is, that will be great! :D