Allen Park — There's no wrong way to build a roster, but if you ask most NFL decision-makers, their preference would be to draft and develop. Draft picks are cheap and re-signing players you develop is the best way to build a stable foundation.
But other avenues exist for teams to add pieces, with the most important being free agency. When your foundation isn't as stable as you'd like it to be, often due to coaching or scheme changes, sometimes you have to spend more on the open market to plug holes or accelerate a transition.