I've been doing competitive battling for a while,and I feel I want to rate this.
Roserade
Seems good.I don't see anything wrong with it.
Lucario
I suggest the ability Justified over Inner Focus.Since you have bait for Dark type moves through Starmie.But it's still your choice.
Garchomp
Ahhhh,Garchomp.The best dragon in my opinion.Since it already have high attack,run a Jolly nature in order to let it out run several pokemon.Replace Rock Slide for Swords Dance if you it's attack to sky-rocket.You can chose Outrage over Dragon Claw if you want more power.And as for it's ability.You have to go with Rough Skin.Since it's,(I believe,)banned in OU.
Starmie
Chose Rapid Spin.Since Houndoom will appreciate it.And uh,what's with Starmies ability?Go with Natural Cure.
Houndoom
I think maybe you should try this set.
Houndoom @ Life Orb
Trait: Flash Fire
EVs: 252 Atk / 4 SpA / 252 Spe
Hasty Nature
-Pursuit
-Sucker Punch
-Fire Blast
-Hidden Power Grass / Crunch
Or could go with what LeBoss said.
6th Pokemon
The suggestion of LeBoss.Scizor seems like a good choice.As Fire type moves will be aimed at it a lot,since it's it's only weakness.Here are two of Scizor's strongest sets.
Scizor @ Choice Band
Trait: Technician
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
-Bullet Punch
-U-Turn
-Superpower
-Pursuit / Quick Attack
If you chose to go with the Mix set Houndoom with Pursuit.You can ethier have another Pursuit user or run Quick Attack.
Scizor @ Life Orb
Trait: Technician
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
-Swords Dance
-Bullet Punch
-Bug Bite
-Superpower / Brick Break
Well,that's all I suggest for this team.