With current team comps will armor usualy be prioritized?

Unfortunately this question is way to broad.

The answer depends on many things, including the champion you play, the enemy team setup and your positioning in fights. Damage type alone is not enough to determine itemization.

For example, if their only AP is LeBlanc you might want to get some MR otherwise she'll pick you off before a hard engage. If, on the other hand, their only AP is Twisted Fate and you are playing safe on the back line, you'll be fine with no MR items.

AoE AP champions usually are best dealt with using Locket since it protects both you and your team (it is less effective against single target AP casters though).

The above of course are valid if your positioning is good (e.g. not getting a full amumu combo on you), which shouldn't be hard assuming good warding.

Another factor is your setup. If you can kite them easily and they would need to invest a lot to get to the backline (e.g. they don't have too many gap-closers or assassins) you could even get away with a tiny amount of tanky items. If they do have lots of assassins, then you might need more tanky items.

So the general rule here is:
Do you expect to get lots of damage from the enemy AP carry? If so, you will need MR as well. Otherwise, you will be fine only with armor and health items (stacking only armor without health doesn't increase your survivability that much).

It's really up to who is the most fat guy. Enemy vladimir's 6/0? Rush MR, take locket, banshee's etc. Enemy Yi's getting free kills off your jungler? Rush armour, frozen heart, Randuin's etc. Enemy ADC getting out of control? Rush Randuin's or Thornmail. Your team is doing fairly well and none of the enemy is fat? You can concentrate on providing more utility for your team, and if you are those tanky supports (Leona, Thresh, etc.) you should be ideally taking armour after your sightstone and gold item, unless enemy AP jungle or AP mid is camping your lane then you might want to take aegis instead. If you are AP support (Lux, Karma) then you should rush sightstone then throw away your gold item (it's not worth it usually to keep it) then go straight AP from there. If you are utility support (Janna etc.) then get some utility based items like Twin Shadows (for scouting and chasing) Locket (for the shield) Michael's (for the free QSS) Banner etc.

In conclusion it's really situational.

Depends of some factors, but they main one here is the current "meta" actually the meta is populated by:

• Top: Tank (Maokai, Gnar)
• Jungle: Tank (Shyvana, Hecarim)
• Mid: carry, AD(Zed) or AP(Ahri) but carry 99% of times, can be support (like Lulu)
• Support: Support is support doesn't change too much, but now here use to have either one with a high stun (Annie) or tank (Nautilus, Thresh, Alistar) if you look at the previous seasons you could see Kayle as support....
• Adc: The main carry, the pool here doesn't change too much, but with reworks, etc the situation changes, actually Sivir is one of the best, and Lucian "is out of meta" but 6 months ago (season 4) Lucian was the best one.

The value of this meta can change with each update from Riot, but usually changes during the change of the season.

Now is the season 5, for example, in the last season all teams tried to invade the enemy´s jungle, but now, we should start by the frog or our golems (sometiemes botlane take the golems, or toplane the wolves) .

Now, why they pick armor instead of weapons, the reason is simple the tanks are "the frontlane" which has to receive all impacts from the enemy's carries, then you have (for the teamplay) to build armor, and the carries only build offensive item (or one defensive).

Also there are some champs (Shyvana, Jax, Irelia, Hecarim) that if you build Randuin's Omen as second item (if the match is balanced) you "can't" die.

But this is the theory and how the pro players play, the situation in Solo Queue is different.