Armaldo has the potential to support its teammates rather than rely on them for a sweeping opportunity, by virtue of its excellent support movepool. One would expect that, with the many ways it can support its team, coupled onto its reasonable defensive stats, and lack of Speed making it a less potent offensive threat than it could be, this would be Armaldo's most used set. However, its typing gives Armaldo a mere two resistances, to Normal- and Poison-type moves, widely accepted as the worst attacking types outside of STAB, and with weaknesses to Rock-, Water-, and Steel-type moves, which is incredibly detrimental. The Rock-type weakness is really the killer, whereby Armaldo obtains the infamous 'Cloyster syndrome' (being a Rapid Spin user weak to Stealth Rock), and this weakness both limits its survivability and also undercuts its utility as a Rapid Spin user. However, this should not discourage you from using Support Armaldo, as it can be a very useful tool when a lot of jobs need doing.
Rock Slide is advised as your attacking option for reliability, though there are always other options. Rock Blast may seem an odd choice when Stone Edge and Rock Slide are available, but it can also be used to support the team in a way Armaldo's other STAB moves cannot. Similar to Marowak's Bonemerang, Rock Blast can be used to break Substitutes; for example, against a Substitute + Toxic Moltres, Armaldo can break the Substitute with its first Rock Blast, then follow it up with up to four more 4x super effective STAB hits. Its accuracy is shaky at best, but then again Stone Edge has the same accuracy anyway. Stealth Rock is, naturally, a useful entry hazard with which to build up damage, and can be useful if you have no other Pokemon on your team capable of setting it up. Rapid Spin removes the entry hazards on your side of the field, which is beneficial to those Pokemon that have to keep switching, as well as those that are vulnerable to entry hazards, including Armaldo itself. Knock Off is best used by removing the item from more specialized Pokemon--walls such as Slowbro hate to lose their Leftovers, and sweepers will also miss the extra kick from their Life Orb or Choice item. Lastly, Toxic can go over either of the previous moves, its main use being to cripple walls, as well as Spiritomb that attempt to block Armaldo's Rapid Spin attempts.
Armaldo is naturally physically defensive, so the EVs serve to reinforce that. Its Special Defense can be patched up with sandstorm if you feel it is exposed, but this may harm your other team members, so be sure to take it into account. The remaining EVs are placed in Attack.
Armaldo can support a great variety of Pokemon with its moves, and so can cater to a great variety of strategies that require adequate support. For example, as a Rapid Spin user it can clear the field of Stealth Rock, which is a great help to Pokemon such as Moltres and Scyther who are quite crippled by it, as well as giving more switching opportunities for Pokemon such as Arcanine. One of its notable advantages over its fellow Rapid Spin users is, on offensive teams especially, that unlike Claydol or Cloyster, the opponent will not always assume that it is a Rapid Spin user, and so Ghosts will not always converge upon Armaldo en masse; after all, even 252/252+ Spiritomb takes hefty damage from a +2 Stone Edge, and Mismagius is not exactly the first choice to defeat the Rock Polish set. Thus, in a similar vein to Kabutops, Armaldo can often find itself clearing the field of entry hazards set up by stall teams, though this facade will only work once, and without the power of the offensive sets, it cannot hope to get past Spiritomb (though Toxic can remedy this). Armaldo will still almost always break a Mismagius Substitute with Rock Blast, however, and more often than not can deal damage past it through consecutive hits.
In the vein of offensive teams, Toxic, Stealth Rock, and Knock Off all hamper the opponent's walls and can indeed aid in a sweep for any offensive Pokemon, yet they also have utility on stall teams as well, so make sure to choose your Armaldo's moves not only on personal preference, but also on what benefits your team the most. In terms of bulkiness, Armaldo is fairly good physically, but a lack of useful resistances as well as recovery hurts it badly, so it is best to relegate him to a simple secondary physical shock absorber. Lastly, it should be noted that although Armaldo certainly benefits from sandstorm, be cautious about its impact on the rest of your team; Armaldo can often play its role more readily without sandstorm than the rest of your team could with sandstorm.