I'm going to build a 20 feet wide hexagon shaped gazebo.I'm looking to get structural drawings of the footings for hollow load bearing columns.Uplift is an issue here.This stucture is going to be in california.I need to show plans to get permits.And I'm not sure where to start.Can anyone please help.

M,
Footer sizing is not a problem if you investigate and plan carefully.
What does the local code call for ?
What is the soil type ?
How far down to bedrock ?
You can buy treated cardboard footer forms quite cheaply in various sizes. They come in both conical and pyramidal shapes. The larger the footprint of the footer makes it less susceptible to settling.
There are multiple ways to fasten your posts to the foundation discussed at length here on the website. Use the search engine.
Use some crushed rock under the footer for drainage.
Deralte (aka Emmett)