Sweepers are Pokemon meant to get a few KOs before getting KOed, sometimes taking care of whole teams. These Pokemon sometimes use set up (Swords Dance, Quiver Dance, Nasty Plot, etc.) to sweep, and others just use raw power or Choice items/a Life Orb. They are usually very fast with good raw offensive stats.
Wallbreakers are similar to sweepers, in the fact that they hit hard and use the same tactics as a sweeper to deal damage. One difference between them is that wallbreakers are for punching holes in Defensive teams, so some are slower but more powerful. A lot of wallbreakers use set up moves to deal greater damage.
Walls/Sponges are Pokemon that can take lots of hits, usually while stalling the opponent. Pokemon with high defenses (preferably HP, Defense, and Special Defense, but that's not always the case) tend to make the best walls and sponges (for obvious reasons).
252 SpA Choice Specs Dragapult Draco Meteor vs. 252 HP / 128+ SpD Shuckle: 109-129 (44.6 - 52.8%) -- 23.8% chance to 2HKO
-2 252 SpA Choice Specs Dragapult Draco Meteor vs. +1 252 HP / 128+ SpD Shuckle: 36-43 (14.7 - 17.6%) -- possible 6HKO
-4 252 SpA Choice Specs Dragapult Draco Meteor vs. +2 252 HP / 128+ SpD Shuckle: 18-22 (7.3 - 9%) -- possibly the worst move ever
-6 252 SpA Choice Specs Dragapult Draco Meteor vs. +3 252 HP / 128+ SpD Shuckle: 12-15 (4.9 - 6.1%) -- possibly the worst move ever
I like using Shuckle as a damage sponge/wall personally, since it gets Contrary + Shell Smash.
Defoggers are Pokemon with Defog, which remove hazards for the team.
Hazard control Pokemon usually have Defog/Rapid Spin for removing hazards.
Defoggers/Hazard Controllers are sometimes offensive and sometimes defensive.
Tanks are Pokemon who can both take hits and hit hard themselves, so they usually have fairly balanced stats. I love using Ferrothorn and Clefable as tanks, personally. Ferrothorn is a Physical Tank, and Clefable is a Special Tank (though the sets I run on them can take both physical and special hits).
Sweepers/Wallbreakers:
Dragapult @ Choice Specs
Ability: Infiltrator
EVs: 252 SpA / 4 SpD / 252 Spe
- Draco Meteor
- Fire Blast
- Shadow Ball
- U-turn
Scolipede @ Black Sludge
Ability: Speed Boost
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Substitute
- Earthquake
- Poison Jab
- Swords Dance
Volcarona @ Heavy-Duty Boots
Ability: Flame Body
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Bug Buzz
- Fiery Dance
- Giga Drain
- Quiver Dance
Alakazam @ Life Orb
Ability: Magic Guard
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Dazzling Gleam
- Energy Ball
- Psyshock
- Shadow Ball
Rain Sweeper:
Kingdra @ Choice Specs
Ability: Swift Swim
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
- Draco Meteor
- Flip Turn
- Hurricane
- Surf
Walls/Sponges:
Umbreon @ Leftovers
Ability: Synchronize
EVs: 228 HP / 164 Def / 116 SpD
Bold Nature
IVs: 0 Atk
- Toxic
- Wish
- Protect
- Foul Play
Shuckle @ Chesto Berry
Ability: Contrary
EVs: 252 HP / 128 Def / 128 SpD
IVs: 0 Atk
Calm Nature
- Shell Smash
- Rest
- Infestation
- Sticky Web
Skarmory @ Rocky Helmet
Ability: Sturdy
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Brave Bird
- Roost
- Whirlwind
- Stealth Rock
Milotic @ Flame Orb
Ability: Marvel Scale
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Skitter Smack
- Scald
- Recover
- Protect
Hazard Control:
Excadrill @ Focus Sash
Ability: Mold Breaker
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Earthquake
- Iron Head
- Stealth Rock
- Rapid Spin
Corviknight @ Leftovers
Ability: Mirror Armor
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
IVs: 0 Atk
- Body Press
- Defog
- Iron Defense
- Roost
Recommended for Rain Teams:
Pelipper @ Damp Rock
Ability: Drizzle
EVs: 156 HP / 224 Def / 128 SpA
Modest Nature
- Hurricane
- U-turn
- Defog
- Roost
Tanks:
Clefable @ Power Herb
Ability: Unaware
EVs: 252 HP / 112 Def / 140 SpA / 4 SpD
Modest Nature
IVs: 0 Atk
- Meteor Beam
- Stored Power
- Cosmic Power
- Wish
Ferrothorn @ Leftovers
Ability: Iron Barbs
EVs: 252 HP / 16 Atk / 104 Def / 136 SpD
Careful Nature
- Leech Seed
- Knock Off
- Iron Head
- Spikes
Ok, and how you build a team of these Pokemon is simple. Pick the ones that synergize with each other the best, such as Kingdra + Ferrothorn + Pelipper for a balanced rain team. Play around with the team, and test it out, changing things along the way. Note that I did not include every Pokemon viable for each role, so make your own sets for different Pokemon and try them out as well.
Hope this helps! :)