both. i might start with an idea on paper, but then i keep notes as i go. i am working on a shrug right now cause i couldn't find any patterns that i liked enough. i am always struck by the lack of simple (minimal, not neccesarily easy) patterns there areN'T out there!
when i make a pattern from my notes, i might revise the pattern to account for things i should have done in the sample i've knit.
i wish pattern makers would make several samples before publishing a pattern. or watch someone make their pattern. recently i have come across too many poorly written patterns lately.