Thanks for your post! I can see that you put a lot of effort in it, that's really appreciated!
To answer your questions, I'm mostly playing against friends and on the online battle spot, so I don't follow smogon standards that much. That will also make battle in the level 50 format most of the time. And I'm not planning to use it specifically for singles or doubles, so something good for both is what I'm looking for.
I like your Archeops. It uses 2 flying type moves, but it's job is moslty to threater fighting types anyway. Endeavor is good idea to work around it's attack drop under 50% health. It's a shame Aerodactyl doesn't learn a stronger flying move :/
Cradily and Alola Golem are definitely 2 pokémon I wanted to include in the team. They were suggested in the sample thread, and I think they both are very important to a mono rock team.
Speaking of that sample team, they also suggest using Shuckle with sticky web. I really loved this idea. It's a nice support for the slower attackers like Alola Golem. I'm very considering to find a place for Shuckle in the team.
Also, worth mentionning... Dusk Form Lycanroc could be a good setup sweeper with Z happy hour (boosting all stats).
You provided a lot of nice alternatives for the team I'd like to build. It's hard to decide which pokémon would fit better the team. Nihilego would be a good option, as my team is only composed of physical attackers.
Thanks!
As far as Shuckle is concerned, I wouldn't suggest it on a semi Trick Room team due to Sticky Webs, which reduces the Speed of opposing Pkm on the ground. This would weaken Stakataka's Gyro Ball and only benefit Alola Golem and Archeops. However, if you think you know when and how to use Shuckle effectively, you could use it as your sixth Pkm. Personally, I would go for a Bold nature and Gluttony + Yapa Berry so that you can play Shuckle more recklessly. Its Special Defense is already high enough, especially with Sand Stream support from Gigalith. With Gluttony and Yapa Berry, you get the chance to set up Sticky Web/Stealth Rock and knock off Excadrill's item. This was just an example.
As for the sample team you were talking about, that Shuckle can support not only Alola Golem, but also Terrakion and Mega Diancie. The last two Pkm have high enough speed to really make good use of Sticky Web. Choice Scarf Terrakion can outspeed Choice Scarf Greninja, and Mega Diancie doesn't have to worry about Choice Scarf Keldeo. If you want to rely on that sample team, I would advise you to look for a Pkm that can deal with Mega Sableye as you don't have Mega Diancie. Minior might help so long its HP are not halved. If it were below half, then it'd be susceptible to Will o Wisp. Choice Spec/Life Orb Dazzling Gleam Nihilego might help, but I think (Mega) Tyrannitar with Subsitute and Dragon Dance might be even more effective as it heavily pressures Ghost and Dark Teams.
Dusk Form Lycanroc is an interesting idea, but it might be difficult to find a good opportunity to use Z Happy Hour as it is very frail and still not strong enough to OHKO certain Pkm such as Celesteela, Gliscor, etc.. But if you want to use it, both Fire Fang and Thunder Fang are a good option. I don't know which one of these moves you ave on Lycanroc, but if it is the latter, I can say that it's helpful to OHKO Keldeo after some chip damage.
For Doubles, I will list off all the Pkm that I find very useful for a Rock Team. Of course, it depends on whether you want to use a full Trick Room team with Gigalith or just a semi Trick Room team.
Aerodactyl: Sky Drop, Rock Slide, Wide Guard, Tailwind | Jolly | Focus Sash | Unnerve | 252 Atk, 252 Speed, 4 SpD
Cradily: Giga Drain, Sludge Bomb, Hidden Power Ice, Earth Power | Quiet | Sitrus Berry/Expert Belt | Storm Drain | 252 HP, 44 V, 212 SpA
Aurorus: Hyper Voice, Freeze-Dry, Protect, Earth Power | Modest | Life Orb/Never-Melt-Ice | Refrigerate | 212 HP, 116 V, 140 SpA, 4 SpD, 36 Speed
Alola Golem: Double Edge, Explosion, Wide Guard, Protect | Brave | Magnet | Galvanize | 172 HP, 252 Atk, 84 SpD
Stakataka: Rock Slide, Trick Room, Gyro Ball, Protect | Lonely | Rockium-Z | Beast-Boost | 252 HP, 252 Atk, 4 SpV
Carbink: Moon Blast, Trick Room, Reflect, Light Screen | Bold | Light Clay | Sturdy | 252 HP, 156 V, 100 Speed
Nihilego1: Hidden Power Ice, Sludge Bomb, Protect, Thunderbolt | Timid | Life Orb | Beast-Boost | 4HP, 252 SpA, 252 Speed
Nihilego 2: Hidden Power Ice, Sludge Bomb, Trick Room, Protect | Calm | Yapa Berry | Beast-Boost | 4 HP, 252 SpA, 252 SpD
Tyrannitar: Rock Slide, Protect, Assurance, Ice Beam | Brave | Mega-Stone | Sand Stream | 252 HP, 84 Atk, 140 D, 32 SpA
Rhyperior: Rock Slide, Drill Run, Protect, Rock Wrecker/Elemental Punch | Brave | Rockium-Z/Sitrus Berry | 152 HP, 100 Atk, 204 D, 52 SpD
Gigalith: Rock Slide, Heavy Slam, Stone Edge, Protect | Brave | Rockium-Z | 244 HP, 252 Atk, 12 D
I don't remember anymore why I choose the EV spread. In most cases, they were influenced by SM, but they should be still useful for USUM. I think Carbink is the only Pkm whose spread is a bit out-dated, but I was too lazy to breed and train another Carbink. This Carbink is fast enough to outspeed Sylveon and Azumarill if I recall right, and set up with Reflect/Light Screen. This is useful when I don't want to use Trick Room yet.
Tyrannitar is strong enough to OHKO Landorus-T with Ice Beam if I recall right, while Cradily requires a boost to do so with Hidden Power Ice.
In case you don't use a full Rock Team, having a Pkm with Intimidate works wonder as the given EV spread of some Pkm allows them to survive 2-4 Earth Quake from Landorus-T.
Team suggestions for 4-4 or 6-6:
1) Gigalith, Cradily, Carbink, Alola Golem (Lunatone/Solrock, Lycanroc-Midnight)
Just make sure one of your Pkm has a Fire move and a Psychic move. Gigalith can use Choice Band to attack with a very strong Rock Slide. As for Lunatone, I haven't used it in Doubles yet, but from my experiences in Triple, it was very good at setting up with Trick Room and threatening Pkm with Ice Beam, Earth Power, Grass Knot, or Psychic. As for Lycanroc-Midnight ... I like it, and it's not bad with Stone Edge, Fire punch, Sucker punch, Protect. It can also remove terrains with its new Z-Move. If you want to use Lycanroc-Midnight, I'd suggest a bulky, offensive EV spread.
2) Aerodactyl, Aurorus, Nihilego, fast Alola Golem (Tyrannitar, Archeops)
Tyrannitar doesn't need to run an Adamant/Jolly nature, but if you want to make use of Dragon Dance (while Aerodactyl Sky Drops an opposing Pkm) or of a Choice Scarf set with Assurance/Rock Slide/Ice Punch/Protect, that's fine too. If you want, Archeops could run Quick Guard to protect your team from Aqua Jet, Mach Punch,Fake Out, or Bulet Punch.