I’m a newbie to freelance design and I need your help. I recently landed a gig with a guy who wants to develop a drink hes been working on. He wants me to do the bottle design and labeling.
I had a few questions I was hoping you guys could answer:
What should I know before I design a plastic or glass bottle?
After the design is finalized, what type of file do I send to a manufacturer?
How do I find the volume inside the bottle in solidworks?
Do you know of any good website or books about bottle design?
Anything else I should know?
Thank You to everyone who helps a fellow designer out. 
See if you can visit a bottling plant that blow-molds PET bottles onsite, and note the limitations and the process of manufacture.
The actual manufacturers of any thing will vary as to what they need. You will have to do a survey of the ones you might actually use, and the ones you might use will depend on… a lot of things, from the quantity made, to the brand being serviced… too many variables. It depends. Universal cop-out answer, but true, here.
There will be a step where the final shape desired determines the shape and size of a bullet or billet, a blank that is injection-molded and then fed into the machine that blows it into its final shape. That will be entirely out of your hands, but it may present limitations that determine final bottle shapes that are not feasible.
Get him to pay you up front. Be wary of promises of how great this will be in your portfolio, shares of his nonexistent company, or other con-artist games.