To brew any potion requires it's recipe, non-magical lists of ingredients and instructions. It also takes time and money. Success is not guaranteed. In fact peculiar or even deadly results are possible. The chance of success can be increased if a congruent spell is cast as a ritual during potion creation.
One day and effect's level*d4*25gp per roll: 2d6 + mods >= 7 potion created "doubles" - Funkyness from bad (12) to good (2) +X brewer's level -X potion effect's level +X matching ritual caster's level
Example "doubles"; 12, poison. 10, Potion of Delusion. 8, potion lasts only 2 rnds. 6, brewer's skin is green d6x days. 4, d4 doses created. 2, double strength.