I don't think Aerial Ace should get its own slot in roost + 3 attacks. I actually think it's Aero's most replaceable move. Stone Edge and Roost are obviously stand alone moves that don't need slashes. I personally use Stone Edge Crunch Aqua Tail roost a lot.
Aerial Ace hits:
Shaymin (Stone Edge does do a lot though)
Celebi (hates crunch)
Roserade (SE is probably close to an OHKO though, if not OHKOing)
Mienshao (Aqua tail does 80-90ish though)
Heracross (Stone edge does a lot)
Chesnaught
Scrafty (I'd imagine Aqua tail does pretty decent damage)
Machamp (I'd imagine Aqua tail does pretty decent damage)
Toxicroak (can also be EQed)
Amoonguss (bolded because it's harder to wear down than shaymin due to regen)
Of this list, Chesnaught is the only thing you're never going to break through. For the others, repeated Aqua tails or Stone Edges or EQs will do the job.
Crunch hits:
Slowbro
Mew
Metagross (can also be EQed)
Jirachi (can also be EQed)
Celebi (can also be Aerial Aced)
Mismagius (Stone edge does a lot)
Azelf (hates Stone Edge)
Starmie (hates Stone Edge)
Trevenant
Bronzong
Earthquake hits:
Mega Aggron (although it still kind of tanks it)
Metagross (can also be crunched)
Jirachi (can also be crunched)
Ampharos (doesn't like repeated Stone Edges)
Mega Manectric (too slow to outpace it anyway + Stone Edge 2HKOs easily)
Empoleon
Nidoking/queen (can also be aqua tailed)
Tentacruel (hates Stone Edge)
Aqua Tail hits:
Hippowdon
Gligar
Donphan
Krookodile
I may have missed some things. The things in bold are the things that you really need the move for - the things that without the move you're going to have a tough time breaking.
I think Stone Edge + Aqua Tail + Crunch gives you the best coverage. So this is how I would set it out:
Stone Edge
Aqua Tail / Aerial Ace
Crunch / Earthquake
Roost
I slashed Crunch with Earthquake because it hits similar targets (Jirachi / Bronzong / Metagross). In set comments you could note how Aerial Ace / Aqua Tail / Stone Edge / Roost is also fine. I didn't slash aerial ace in both the 2nd and 3rd slots because it looked messy to my eyes.
Basically, I don't think Aerial Ace is enough of a no brainer to warrant a moveslot of its own. Happy to hear opinions from other ppl about this though.
- Best way to utilize Mega-Aerodactyl
I don't like this statement. Defog and 3 attacks roost do different things. I don't think either is best.