Here is a list of the rolls on our team. There could be a few others, but this is the basic setup that most teams should be trying to get to. I did not list the numbers needed in each roll as all teams are different sizes.
Squad Leader – Hardest job in the squad. Needs to be able to command the squad and get them to react under fire.
Automatic Rifleman – Generally uses an m249 or m60. They lay down the main cover fire for their team and generally hang back.
Designated Marksman – Either uses a bolt action rifle or a semi auto m16 or SR-25. Might go off as a recon sniper, but mostly stays with their squad. Their job is to take precision fire when necessary.
Grenadier – Uses a m203 rifle or stand alone grenade launcher. Best used to clear a room from the outside or to deal with multiple enemies on a hill. The grenadier can instill almost as much fear into your enemies as a soldier humping a SAW.
Medic – Generally carries a light rifle and medic pack to dispense treatment to downed teammates. Very useful when there are medic respawn rules in effect.
Demolitions/Heavy Weapons – Similar to the Grenadier, but uses hand grenades and claymores and maybe even rocket launchers. Main roll is to set up ambushes and rear defense. Secondary would be to help clear rooms. If there is a target that needs to be blown up to complete a mission, this is the person that would be carrying the explosives.
Rifleman – The most common team member. Evey team needs many riflemen. Their roll is to provide fire on the enemy, and movement to flank positions.
Did I miss a roll? Let me know in the comments.