Question: The Artificer in our party has the ritual to brew common potions, but we are trying to figure out what he needs to learn to brew uncommon potions. Below is the ritual.

> 
> Brew Potion
> 
> 
> Liquids brew and bubble, coalescing the raw substance of magic into a form you can drink.
> 
> 
> Component Cost: Special
>  Market Price: 75 gp
>  Key Skill: Arcana or Religion (no check)Level: 1
>  Category: Creation
>  Time: 1 hour
>  Duration: Permanent until consumed
> 
> 
> You create a common potion or elixir of your level or lower. The ritual’s component cost is equal to the price of the potion or elixir you create.
> 
> 
> 

And the errata:

Update (11/17/2010)
In the first sentence of the ritual’s effect text, replace “potion” with “common potion or elixir.” In the second sentence of the ritual’s effect text, add “or elixir” after “potion.”

Answer: 
Typically uncommon items are only found, not created or purchased. 

However, this does not preclude you (or whoever the DM is) from providing the player with the brew potion recipe with the recipe he would need to brew an uncommon potion (although the ingredients could potentially be harder to find, more expensive than the potion).

Much like many DMs allow for the purchase of uncommon items under special circumstances, this would allow for the creation of uncommon potions when the circumstances were right for allowing for it.
Not RAW: I found the restriction to "only common" for creating new items a little restrictive, and allowed PCs with creation feats to have one item per level from the uncommon category, and once per tier the character could create a rare item. I found this more convenient than focussing on details of how this was achieved (in my campaign I did not have table time available to consider adding many side quests)