My suggested implementation:
Step 0: No golems: The default state is that you can't make golems.
Step 1: Artifact golem: "golem" is one of the types of things that can come out of a strange mood. The golem will (usually) be mysterious, and whether this becomes a good thing or a bad thing will depend on various factors, such as the type of mood, the source of the inspiration, the mythological connotations of the materials used, and what you do with the golem. Depending on the nature of the golem and the process of its creation, the dwarf who made it may be able to just go ahead and make more (Step 2). Maybe not, though; don't count on it. If she doesn't have that ability, you will first have to figure out if it's even possible to just make more; to do this, you have some skilled dwarves examine the golem, and try to figure it out. Most of the time, they won't, but sometimes, you'll go to Step 3.
Step 2: Urist Golem-Maker: If your formerly-moody dwarf can make more golems, then she can just do that, with the exact process and materials procedurally generated based on various factors, such as the type of mood, the inspiration, ... you get the picture. Generally, you will need whatever went into the first golem, although some parts may be superfluous, and some parts may have been divinely provided and need to be replaced with rare/expensive/bizarre substitutes in the production recipe. Urist may or may not be able to train more golem-makers. If she can, you can go to Step 3.
Step 3: GolemMurdered: Once Urist trains a certain number of golem-makers, it will just sort of be assumed that dwarves in her fort can become golem-makers. Generally, if you survive long enough, you will be able to progress to Step 4.
Step 4: Golem-making Civ: Once a site has enough aggregate golem-making training, the skill can start spreading into the general skills of its entity.
Step 5+:
: I don't feel like going further right now.
Sometimes, your civ will start out on a step higher than zero. Also, most of the time you won't get a golem at all, even in a ten-year fort, and even when you do get a golem, it's still rather likely (P>0.5) that you won't be able to make more.