Thinking of writing a beginner's guide to competitive Pokemon for a couple of friends and just for the craic, and I'm currently writing about the "roles" a Pokémon could have on a team. While still being quite simplified and not taking into account things on a Pokemon by Pokemon basis, would it be fair to say these ten are the basic roles you could have filled in a team:

Fast Physical Attacker
Fast special attacker
Fast mixed attacker
Bulky physical attacker
Bulky special attacker
Bulky mixed attacker
Physically oriented wall
Specially oriented wall
Support (Fortification) - ie: screens, defog, heal bell
Support (Hinderence) - ie: stealth rocks, toxic, string shot