Ask HN: How to charge for consulting and support?

I have a client who is asking me to automate a deployment into cloud and also asking if I will support it once it goes live. This is my first consulting gig and I don't know how to bill. Can anyone give some tips please ? I was thinking something like X$ to get the build automation and go live and then every month charge Y$ for fixed hours of consultation ? I am confused what to propose.