We recently had a situation come up in game where my wizard cast flaming sphere from a scroll. He rolled it over a troll who then had to make a reflex save. My question becomes what is the save DC since I don't know the INT score of the wizard who wrote it? Does it use my INT score, or the minimum int score needed to cast a second level spell (12)?
It'll use the minimum Intelligence score. You can make things with higher scores, but it's easiest to presume the minimum, so the DC should have been 13.