I WANT to kick this team in the nuts, but I'm gonna be nice about it.
First off, proper RMT format includes EVs, natures, and items in addition to what you've got up now. An RMT should be for a team you've already run through a couple of battles and can't seem to fix for whatever reason, or if you just wanna brag... Needless to say, you should already HAVE six Pokemon here.
Pokemon Name @Hold Item
-Move1
-2
-3
-4
Ability, Nature
EVs
(Description of what the Pokemon is supposed to do, and problems you are encountering with it.)^ Basic format. No, it doesn't have to be in italics. On another note, you should list your LEAD as the FIRST Pokemon.
Now, onto the actual rating.
Everything in your team right now is weak to Fire! Seriously, considering that a max Sp.Def Cloyster is OHKO'd by a Pachirisu's Thundershock (120 power with STAB and weakness), it and the rest of your team wouldn't stand a chance against a Scarfed or Spec'd Typhlosion (Eruption = 225 power after STAB, weakness and resistance), and an Infernape could probably even threaten to OHKO Lucario with Vacuum Wave if it Nasty Plots up against the Roserade (assuming you'd Sludge Bomb, Toxic Spikes, or switch first thing).
Roserade (I decided to make my RMT somewhat fancy for lack of anything else to do right now).
First off, I'll note that Roserade probably doesn't belong here in the first place. Roserade's specialty is setting up Toxic Spikes early-game for stall teams. Besides the fact that your Roserade isn't built well for setting up Toxic Spikes, you're not using a stall team, and there are Pokemon in OU that can do it much better (since it looks like you plan on taking this team into OU).
If you insist on sticking with Roserade as your lead, I would suggest giving it Sleep Powder to shut-down opposing leads before attempting to setup Toxic Spikes. Since you're not running a stall team in the first place, though, I would run a more sweeping oriented set.
Roserade @Choice Scarf
-Sleep Powder
-Sludge Bomb
-Leaf Storm
-Hidden Power Fire
Natural Cure, Timid
252 Sp.Atk, 252 Spd, 4 HP
A set like this is primarily geared towards shutting down the enemy lead and then switching out to an appropriate setup Pokemon or something. Late-game, it can come back out to sweep with Sludge Bomb, or take out threats in a hit-and-run fashion using Leaf Storm, which compliments the Scarf, since it has to switch out, anyway.
Tip: When it comes to team building, the first thing you do (or at least the first thing I do...) is pick a lead. Once you have a lead chosen, the rest of the team is usually cake, because you just need a Pokemon that covers the weaknesses of the last. For instance, Roserade is weak against Fire, Ice, Flying and Psychic. So, you just need a Pokemon that can resist as many of those types as possible, and deal with potential threats accordingly. Steel types resist Ice, Flying, and Psychic, but they're also WEAK against Fire, like Roserade. Empoleon, Bastiodon, Probopass, Aggron, and Heatran on the other hand don't take any Super Effective damage from Fire, while still resisting the other types of attacks fairly well. Metagross
I'm gonna have to agree with Ryu here. Metagross probably shouldn't be running both Meteor Mash AND Bullet Punch, and there's NO reason to run Psychic. Metagross isn't really meant to be super-speedy or anything to begin with, but it CAN run Agility very well. I'd sooner run Bullet Punch than Meteor Mash, and DEFINITELY pack EQ over Psychic. The last moves could be any combination of Thunder Punch, Ice Punch, Explosion, or Agility. However, I wouldn't immediately cast off the potential worth of a Choice Band set, which COULD do very well, depending on how you use it- Metagross also gets Trick, which could allow you to trip up some walls.
Metagross @Life Orb/Leftovers
-Agility
-Meteor Mash/Explosion
-Earthquake
-Thunder Punch/Ice Punch
Clear Body, Adamant
112 HP, 252 Atk, 12 Def, 132 Spd (Pretty much Smogon copypasta cause I'm lazy).
Here's a standard Agility Metagross set. Basically, Agi up, sweep. Smogon says Agi, MM, EQ, and either one of the Punches or Explosion, but EQ and Ice Punch have good coverage, and you can Explode on anything that might actually wall you, soooo... Yeah.
Tip: On most sets, if you don't have an item that would directly benefit the Pokemon or its set, Leftovers is usually a pretty safe choiceLucario
This set actually isn't bad, but it's pretty hard to screw up Lucario since everyone wants to give it ExtremeSpeed and Close Combat, anyway... You don't really need Aura Sphere at all (I would sooner replace it with Vacuum Wave or Bullet Punch), but you can use Dragon Pulse to bait Blissey, then OHKO with Close Combat or something... To call Lucario a "pawn" is a SEVERE under-estimation of its potential. Lucario is one of the best wall-breakers in the game right now, period.
Lucario @Life Orb
-Dragon Pulse
-ExtremeSpeed
-Close Combat
-Swords Dance
Inner Focus, Jolly
252 Atk, 252 Spd, 4 HP (One extra point of Sp.Atk doesn't make any difference.)
After doing a few calcs, well... This set could work out all right. Dragon Pulse does enough damage to Salamence and Dragonite that an ExtremeSpeed can take them out almost 95-98% of the time afterwards WITHOUT a Swords Dance, assuming max HP and Def/Sp.Def IVs on the Dragons' ends, and minimum damage for both attacks on Lucario's end. FatMence and BulkyMence would murder it, though- of course, these scenarios assume that you haven't given away the fact that you've got Dragon Pulse yet, and that they Dragon Dance up, assuming you'll switch, in which case ExtremeSpeed finishes the job.
Tip: Mixers love Life Orb- at the cost of just 10% of your health for every direct attack, you get a 30% damage boost to both Physical AND Special attacks!Froslass
Once again, Ryu's right. Froslass REALLY hurts this team. Besides the fact that Cloyster's the only Pokemon on the team which is immune to Hail (aside from Froslass itself), the fact that it takes a turn to set up is painful enough. Also, Froslass is pretty easily walled here by, well... Any given Water type. Froslass is built primarilly for Hail teams, and there's a VARIETY of Ghost types open to you which can fill in for Froslass much better- Gengar comes to mind. If Froslass has any advantage here, it's Ice Beam and Destiny Bond. Froslass is best left as a Spiker suicide lead or something.
Froslass @Choice Scarf
-Ice Beam
-Shadow Ball
-Thunderbolt
-Destiny Bond
Snow Cloak, Modest
252 Sp.Atk, 252 Spd, 4 HP
I went to the bathroom, wiped, and this was the skidmark left on the TP. Scarf'd revenge killer, I guess. BoltBeam for good coverage, Shadow Ball for STAB, Destiny Bond for taking things out late-game. You could also run Trick to trip up Walls and such...
Cloyster
Cloyster's really not THAT bad... But a lot of people don't use him for a reason. There are plenty of Pokemon that do what Cloyster does much better. STAB'd Surf and Ice Beam can be useful, since they've got pretty decent coverage together, but he's left to run a Hidden Power or Toxic to cover other Water types, which could probably KO pretty quickly by means of Surf. On the other hand, it could help deal with threats like Gyarados and Swampert, which tend to run physical sets, and counter with Hidden Power Electric or Grass. Since it's not too terribly slow, either, it can run Icy Wind pretty well against switch-ins, and then Explode on their faces.
Cloyster @Leftovers
-Surf/Rapid Spin
-Hidden Power Electric
-Icy Wind
-Explosion
Shell Armor, Naive
252 HP, 196 Sp.Atk, 60 Spd
With this Cloyster, you should be able to switch into oncoming physical attacks, and force switches. If you figure they're gonna switch, you can Icy Wind for a Spd drop and react accordingly, either Surfing, Exploding, or switching. If you're up against a Gyarados or something, Hidden Power Electric will 2HKO. With the Spd investment here, Cloyster can outspeed Pokemon like Lucario after an Icy Wind- Pokemon that max at 306 Spd. Things like Blissey and Roserade you should be able to easily Explode on. Surf and Rapid Spin are both options against Swampert. A Swampert will likely be setting up Stealth Rock for the team, so you could Rapid Spin, Surf when they try to set it up again, Rapid Spin once more, and then Explode on their face.
As for some final tips...
Well, you don't have to worry about Electivire... At all. I'm pretty sure I'm the only person to have used one in OU in, like... A long time. Same goes for Weavile, no one uses it.