I wouldn't say I make premade plots, but much of what bounces in my head is a detailed context and set of characters where someone  else can throw their own character into and change the dynamics. I believe I do a fairly good job of letting folks carve their own paths, and my ideas for a particular story/character shift on minute details all the time. That said, I'd probably just leave them vague, and let the lore/details come out upon the RP's start.