I will try to clarify the whole Construction of magic items here.
At various levels of construction magic, you get access to new and more powerful magic items. However you don't have a list. This is for two reasons:
1) You may want to devise your own and a list may feel restrictive.
2) The list is really big and finding which item is better than which would be a real pain.
Generally speaking, one mage can forge 1 mana worth of magic items per update. These can be equipped by a unit in case of boosters (research or magic), or per individuals (like your pretender, heroes, or one of your soldiers). To be fully equipped, an individual will require 2 mages and 2 mana, or even 3 for top-notch equipment. That includes magic weapon, shield, armor, helmet, boots, rand a pair of miscellaneous items like rings or bracers.
To make things complicated, some nations have better output than others (Ulm for instance) so they get 25% more items per mana.
Now let's say you want to kit a unit of several soldiers, how many gems do you need?
Unfortunately, it depends on the unit. In general, consider that, for magic item purposes, 1 unit of wizards or assassins is 3 individuals, and 1 unit of infantry is 10 individuals.
If you're playing giants, that's less. If you're trying to kit summoned monsters (preferably humanoid, since other creatures usually can't get any armor or weapon so they might only get a few trinkets), it depends on the creature type. 1 summon may require to equip 1, 2 or 20 creatures, depending on their actual numbers. For instance 1 unit of behemoths is 2 creatures, but 1 unit of jaguar toads is 20.
Let's say you want to equip your creatures with some equipment. The best way to do it is to ask me to forge items that 'increase their defense' for instance, I'll then give you a pendant of luck or an armor depending on the unit and the mages you have.
I can simplify the rules a bit:
Unless you want to devise your own magic item with its own special effects (and sometimes even then), if you want to kit an individual or unit, you tell me how much mana you spend. 1, 2 or 3 per individual, and with what focus. In the stats, I'll just note that the individual or unit is equipped with 1/2/3 mana worth of construction level X magical stuff.
You can kit:
-an individual (1, 2 or 3 mana)
-a whole unit (10, 20 or 30 mana for an infantry unit; 3, 6 or 9 for a wizard unit)
-part of a unit (from 1 to 29 mana for an intantry unit, 1 to 8 for a wizard unit: means all individuals don't have the same equipment and it's sprinkled a bit here and there).
If you really really want to know how it works, 1 mana = 20 gems in the game, so 1 mana buys you that much worth of magic items, but not all items are available and you can make your own.
If you want to optimize your equipment, it's going to be nightmarish, I'd rather avoid entering this level of detail. I don't think a god or the ruler of a nation is interested in knowing exactly the kind of weapon, helmet and boots his soldiers wear so I'd rather keep it abstract (like: 1mana of anti undead offensive gear, 2 mana of equipment for long fights, 1 mana of equipment to make spells more efficent).