Since you already have the beginnings of a Sunny Day team, I'll show you a SD team I made up recentely:
Crobat (M) @ Heat Rock
Trait: Inner Focus
EVs: 6 HP / 252 Atk / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Sunny Day
- Taunt
- Protect
- Brave Bird
Infernape (M) @ Focus Sash
Trait: Blaze
EVs: 76 Atk / 252 Spd / 180 SAtk
Naive Nature (+Spd, -SDef)
- Fake Out
- Mach Punch
- Heat Wave
- Protect/Encore/U-turn
Garchomp (M) @ Yache Berry
Trait: Sand Veil
EVs: 4 HP / 252 Atk / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Earthquake
- Rock Slide
- Dragon Claw
- Protect
Cherrim (M) @ Leftovers
Trait: Flower Gift
EVs: 252 HP / 164 Def / 92 SDef
Calm Nature (+SDef, -Atk)
- Solarbeam
- Sunny Day
- Protect
- Helping Hand
The moves on Crobat can be changed so that it fits your already-bred Crobat better (Brave Bird replaced with Heat Wave, Jolly replaced with Timid, EVs switched from Attack into Special Attack), and the last move on Infernape is up to you. Protect is great for predicting (especially with Focus Sash, allowing you to survive another turn at 1 HP and waste your opponent's attempt to kill Infernape). Encore is nice against teams that try to set up, but you need to be faster than the pokemon you are Encoring (so that you can ensure you trap them into a bad move). This makes it rather situational. Another way Encore can be used is to use supreme prediction and Encore a Protect/Detect from your opponent on the turn that they use it. U-turn is another option, allowing you to hit an opponent and then switch out safely.
The main strategy is to get Sunny Day set up with Crobat so that Cherrim and Garchomp can come in at the same time and destroy with Flower Gift + Helping Hand. This gives Garchomp a 1.5 boost to his considerable Attack value and another 1.5 boost on the damage calculation. The EVs on Cherrim allow it to survive two Flower Gift + Helping Hand Earthquakes from Garchomp due to its' handy Ground resist, and Rock Slide has the nice flinch chance when you are facing fliers or don't want to hurt Cherrim. Cherrim can also serve as a backup Sunny Day user, and has Solarbeam to take advantage the sun as well.
If you see something you don't like in your opponents' leads, you can use Fake Out + Taunt to stop them. Crobat is useful in that he cannot be flinched, by Fake Out or by other means (Fling, etc.) Against Smeargle + Dusknoir, use Fake Out + Taunt, aiming Taunt at Dusknoir. If they use Follow Me with Smeargle, finish it off next turn with Mach Punch and Taunt Dusknoir. Now, although they do have TR set up, you can attempt to stall it out with Protect, Focus Sash, and other such things while you set up Sun for when TR ends. Try to kill Dusknoir or Taunt it again if the first one runs out before Crobat dies, or he will set up TR again as soon as the first one ends.
Again, it's not perfect, but you have some of the pieces already, and you seem to like the idea of a Sunny Day team. If anyone has any suggestions to improve this team, I am very open to new ideas.