What your client wants is the definition of RING or NEST cam.

What you need to do, is educate him on why that is a bad idea.

1) Internet goes down, no recorded footage (that includes someone killing their internet on purpose). This alone should be enough.
2) Quality and capture is dependent on upload speed. The more cameras you add, the more saturated the connection. And the lower the quality of the captured video becomes. And higher chance of it missing the recording.
3) Privacy issues.
4) Monthly fees.

Cloud based CCTV has it uses for remote locations and special circumstances.
But for it to be a 'go to' for CCTV is f^n stupid. But again, look at the hordes of people flocking to it these days. All I can do is shake my head.