Vatlings

As previously stated, sorcerers grow artificial bodies in order to duplicate spells. Typically, very short-lived homunculi are used, lasting just long enough to get the job done. Some sorcerers create longer-lived homunculi via this process however, commonly referred to as vatlings. Here's a system for their creation accompanied by some bad scans of crappy watercolor splotch drawings I made.

The demon-flesh samples used to grow vatlings are contained in specially-constructed zinc cylinders that stabilize the tissues for long-term storage. They're expensive to create and feed, so mostly sorcerers make do with a handful of strains, but if a new mutation is particularly useful it can be tempting to add to your repertoire.

When finding a new tissue sample (from another sorcerer), roll random characteristics for the fleshy shells that strain creates (or just make something up):

Reproduction:

1	Spores (either)
2	Egg-laying (sexual)
3 – 5	Budding (asexual)
6	None

Abilities (2/6th chance of one):

1	Fast maturation (half growth time)
2	Armored skin (+2 AC/Armor)
3	Allergic to gold
4	Burns in daylight
5	Sees in dark
6	Rubbery skin (+1 AC/Armor)
7	Fast
8	Vicious claws
9	Slow Regeneration
10	Wings
11 – 12	Stable (half chance of physical mutations when reproducing)

Appearance:

	Color	Build	Head
1	green	emaciated	no horns
2	chartreuse	skinny	one small horn
3	orange	medium	two small horns
4	magenta	rotund	two horns
5	purple	fat	two long horns
6	blue	obese	two imposing horns

When a strain is used to create a new body, roll 1d8 to see if it mutates:
    1      Change method of reproduction
    2-3   Add random ability
    4-5   Lose random ability
    6-8   No change
And move two of the appearance categories one notch.

It brought you flowers?

Animal material can be added to a tissue sample when creating a new body to give it similar characteristics (like feverlings). Whether special abilities are duplicated is up to the DM, but this would likely increase the material cost at the least.

Vatlings get cold too

Costs:
Base 50 gp * spell level
Size: 1.5' tall and 1 HD per spell level
Lifespan: 3 hrs / 3 days / 3 weeks / 3 months / 3 years / 3 decades / 3 centuries
Cost doubles each category you go up in lifespan
Time to create: spell level number of days, doubles at each lifespan category
Takes twice as long without a proper lab
For each offspring you induce it to create pay the material cost again.
Reproduction is triggered by introducing certain chemicals to the mixture, they don't just start budding while walking down the street.

The smarmiest vatling

So, a body only capable of holding a level 1 spell that lives only 3 hours after creation costs 50gp and one day of labor.
A body for a level 3 spell that will last 3 months would cost 50 * 3 * 2 * 2 * 2 =  1,200 GP and 24 days to grow. It'd be 4.5' tall and HD 3.

Tired of your shit Pamela

You can make a body larger than it needs to be.
They can cast themselves once per day.
They get personalities over time, but start off automaton-like.
Their appearance is rapidly modified by whatever spell they contain (smoking coal-mouths for fireball, etc).
New ones don't automatically like you! Do a reaction roll with your level - their level as a modifier. Bad reaction rolls result in them trying to escape or murder you.

Helping!

Uh yeah that's all I got for now. I'll probably change stuff when I run it and realize it's broken.