Making items magical

There are few things as potentially destabilizing to a D&D campaign as introducing a poorly considered magical item (or, god forbid, artifact). Which is of course exactly why players want to make them - they need all the advantages they can get!

Rules for making magical items can be difficult to draft but they are somewhat necessary for a Gygaxian Naturalist DM who wants to explain where all the magic swords and rings in the campaign world came from. The most open route is to go where 3E went and have Feats, costs and markets clearly defined in the DMG. This sort of sucks the mystery out of what's supposed to be magical though. The more mysterious and magical but very restrictive answer is to say "They were made by Arch-Wizards of the Old Empire, in the days before the Art was lost. No one living today can recreate them." That's certainly very Vancian and post-apocalyptic, but it also sort of sucks the wind out of the sails of the player's enthusiasm. It also doesn't explain the abundance of consumable potions and scrolls, which you would have thought would have been all used up since the days of the Old Empire.

Just recently though I came across the fantastic idea of "Sword Spirits." 

Interactions between magic, Nature, Chaos, and the gods (at least some of which owe their own existence to a process similar to the way the universe formed) has given rise to a variety of elemental beings, not all of which are as insensate and uncaring as Nature itself. I'm currently toying with the notion that the process of metalworking, which involves (to some degree) the interaction of all four elements inadvertently gave rise to a "fifth elemental" -- spirits that are sometimes drawn into crafted objects, endowing them with magical powers and, in many cases, allow the spirit to exercise its own intelligence and will.

The hows and whys of the process I prefer to keep strange and mysterious, including why it is that these metal spirits seem to manifest most fully only when drawn into swords -- thus giving rise to their more common name: "sword spirits." But I very much like the idea that the fashioning of magic weapons isn't simply a matter of a magic-user deciding to do so by following some hoary formula that always results in a sword +1, +2 vs. lycanthropes. I want magic weapons to be, on some level, accidental in their origins, something beyond the ken of men, elves, and even dwarves (who were probably the first to notice the phenomenon). It makes magic swords special and a little bit dangerous and that's a good thing.

A very good thing indeed! Bloody brilliant. 

I would riff off this idea to say that very, very few of the permanent magical items in existence (other than maybe some older artifacts created by the Old Empire of course) were created completely on purpose. At most the caster can influence type of spirit summoned into the item, but the final abilities would be somewhat random. Naturally we would have random charts to determine the results!

Quickly categorizing items

Scrolls, potions, dusts and creams - anything of the "Use once" variety - should be producible without too much difficulty. A good start might be one week and 100 gp/level for making scrolls. Potions and reagents would take a similar amount of time but require a stocked Alchemistry lab and cost more. The DM can of course also limit the ability to make these items by restricting access to the necessary materials. "Yes, you have the money - but no one has a roc feather quill to sell you! And aren't you out of weresquid ink?"

Permanent items would need a master craftsman (probably not the wizard), the finest materials, and the right invocations. Costs would be high. At the end of the crafting and casting a Sword Spirit is summoned and hopefully decides to reside in the item (insert chance of failure here). If it does reside in the item the DM should roll for the puissance (+1 to +5), alignment and Intelligence (if any) and abilities of the spirit in the item.

As an example of influence might be, say you wanted to create an enchantment/charm item - try including a branch from a Dryad's tree freely given, or if you wanted to make an item good vs. lyncanthropes you might toss in the tears of a werewolf's victim and a sacrifice to the Moon goddess. The DM would value the worth of the "influence" and you get the result you want if you roll within +/- X% on the chart.

As for charged items, I am not a big fan. A Wand of Fireballs should, in my opinion, increase the damage, range or area of effect of the Fireballs you cast, not have Fireballs within it. But if you wanted charged items by the book I would make them halfway between scrolls and permanent items.