How to put a sidewalk on a slanted hill?
If you’re working in the “Right-of-Way” you’d better contact the City and verify compliance with their Standards for Construction”. 

The notion that the sidewalk needs to comply with ADA is nonsense, if you’re located on a 30 degree slope. First, ADA is for public “use” building sites, and second it’s not required for extreme sloped sites that create a hardship. 

However, the City will have many requirements and you’ll need a permit to work in the right-of-way, including how and when you can block off the roadway to perform the work.