Not as easy as it seems. You need to determine the individual power lines to each room i.e. for the 13A sockets and lights. Some developments the developer uses a shared system i.e. one MCB to a few power points, perhaps from one room to another to save cost. Not so ethical (due to lax checking) but still workable as long as not too much looping. But from your DB box size, I suspect a few points are looped.

And of course it is not cheap to install the meters (not credited digital ones easily cost above rm200/unit). Somemore you need to do internal wirings and stuff like that.

Suggest you kill the idea and talk nicely to your tenants to save electricity and the Earth