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You did not mention what kind of meters you are intending to do. Analog or digital meters ?
Since analog meters are so simple, they do not need a schematic. In fact all you need is a resistance in series (voltmeter and ohmmeter) or in parallel (ammeter) with adequate value to change the scale of the galvanometer (microamperimeter).
Good starting point is to obtain some 50 or 100uA (full scale deflection current) microammeters and you can build volt/amp/ohm meters. A good laser printer to print the new scale is desirable. Learn about the formulas to calculate the resistance used to change the scales (they are simple, but you need to know the internal resistance and the full scale current).
For digital meters, there are a imense variety of ways of doing it. You can choose dedicated ics like ICL7107, CA3162, etc (search in the Google). A good alternative today is to use microcontrollers, as most of them have Analog to Digital converters, that facilitate their use in voltmeters.