Go down and talk to the people who will be approving (or not approving) your plans.
Maybe in theory, you can design it yourself, in practice it may be painful and frustrating (or it may be easy as pie but "Los Angeles" makes me a bit doubtful).
To put it another way, you can design and build your own bicycle but their might be undesirable consequences of a lack of expertise/experience.
Disclaimer, I have a background in construction and architecture and once worked in a building department and before that a planning department. Good luck.
