Should I make my girlfriend sign a lease?

[Adam Pierce]

Hi BP,

So I'm planning on buying my first home around the end of the year and I would like to allow my girlfriend to live with me. 

We have been going out for about 6 months and I was wondering if I should create a rental agreement and treat her like a tenant, or consider her like a spouse and just hope for the best if things don't work out. 

Additional notes:

I live in CA. My girlfriend won't be putting any money into the property and won't have her name on it. She has a steady job and can pay the needed rent.

Any advice on this will be greatly appreciated. Thank you!