I think many localities require a signed plan from an architect or engineer before you get the okay to pick up the tools.
But there are other localities that don't, and they do their own code review before they approve them. So anyone can draw the plans, and the city will tell you if you need to make any changes. Your tax dollars at work.
Where I live, you don't even need to submit plans -- you just tell them how much you're going to spend and they give you a permit. It's all about the taxes. They inspect the foundations and maybe the electric. Building a new house I think they look a little more closely, but it's pretty lax for additions and renovations.