I've seen there exists some kind of improved armor (for example see Leather Armor +3). But I am unable to find anything about this in the DM guide or PH. Is that official or common homebrew stuff?
And: If I'm having for example a leather armor, how would I go with improving its quality to +1, +2 or +3?
I'd think it could work to search for an NPC who can craft this and let him do the 'upgrade'. But at which costs? It could also be possible to have them as magical items (thus the increase in AC) and to loot them or have an arcane crafter enchant a normal armor.