The role is still pretty wide. Mesmer alone can be anti-caster(domination), anti-melee(illusion), and also use Inspiration to get energy regen. Rangers have even wider diversity. Sometimes I want to many skills that the attributes get spread too thin, may cause yourself some damage in terms of lower skill effectiveness.
If you really have no idea, I would recommend playing it for some time. You will acquire new skills, then try them out, see which type of playing style you will like. Don't forget sometimes people pick out their primary profession mainly because of the primary attribute related skills. So example Rangers, Expertise, it reduces costs of some skills. Can go as high as 50% energy cost reduction.
I wouldnt worry about armor too much unless you are a warrior. If you are caster or range attackers, play it well, keep your distance, you should not have much trouble.
Later you will discover that quite a number of skills, can cause damage that totally ignores armor. But if you want to use primary profesion for deception, that is also a good choice. For example, play a ele primary and a monk secondary. You can pump points into Energy storage to have tons of energy, and other points all go to monk skills. That way, you look like a elementalist but is actually a main healer. Dressing as a monk can put yourself as priority target at times in certain situations.
Dont forget, rangers have 25 base energy. Mesmers have 30. Rangers can get up to 31 wearing druid armor. Mesmers can get up to 42 using off-hand focus item which increases energy storage. Well, rangers too can use off-hand focus item, but you wont be able to use bows then. Bows are 2 handed so you cannot use off-hand items, unless you ranger is just a disguise. =)
My best advice for now is, play the game for some time first. Try out the different skills. You may not get it right the first time, dont worry. You have refund points.
EDIT: heres a little something else to add.
About builds, there are 2 types of builds. Or maybe 1 build definition, another is called profession.
If you want to count the mixtures of professions alone, there are probably already mentioned as above. R/Me, Me/R, Ele/Mo, etc.
If builds in terms of skills or playing styles, there are numerous of them.
R/Me alone can mean many things. You can be anti-casters, anti-melee. Perhaps an all-rounder disrupter, damage dealer perhaps? Within each of these builds itself, the choice of skills is also plentiful.
Take anti-caster for example, it is possible to use anti-casters skill from either mesmer profession or ranger profession or both. Sometimes depend on energy costs and skill type. So its pretty much can be anything. Happy playing.
