The DC to create a magic item is 5 the caster level for the item?. Failing this check means that the item does not function and the materials and time are wasted. Failing this check by 5 or more results in a cursed item (see Cursed Items for more information).
Note that all items have prerequisites in their descriptions. These prerequisites must be met for the item to be created. Most of the time, they take the form of spells that must be known by the item's creator (although access through another magic item or spellcaster is allowed). the DC to create a magic item increases by 5 for each prerequisite the caster does not meet. The only exception to this is the requisite item creation feat, which is mandatory. In addition, you cannot create spell-trigger and spell-completion magic items without meeting their spell prerequisites.
Looking at it though, if you can brew potions, it can be very worthwhile to create those of spells from off your list.
Potions below 250gp require only 2 hours base to create.
Assuming that adventuring is a disruptive environment, this time is doubled.
By taking a +5 to the craft DC, this time is halved.
As potions are use-activated, not having the spell is merely a +5 to the craft DC.
For a 250gp cost potion, you're working with a maximum CL of 5 to begin with.
So Craft(alchemy) DC 5+(CL) +5(fast creation) +5(missing spell) = DC 20 to make a CL 5 quick potion worth 250gp.
A level 7, int focused Expert could pull it off, with a skill mod of 7(ranks)+3(trained)+5(int)+2(mw Lab)+2(Master Craftsman) = +19. Feats required Master Craftsman(alchemy) and Brew Potion.
Handy for popping out low level potions in a hurry, for spells you don't even know, and even an NPC can do it!