I also decided to pay attention to the aesthetics of this project and build one that had a steam punk look.
Rather than simply mount the plastic meters I decided to remove the movements and reassemble them in a wooden case and make my own numbers for the meters with a piece of tea-stained paper and an old typewritter.
From Simple to Complex
The basic design requires only 4 components. A cord, an outlet, a volt meter, and an ammeter. My design is more complex because I have two ammeters and three outputs, each with an independent switch.
Volt meters are connected across, where the current travels and ammeters are connected through the path of the current. (See picture two)
The idea of using a steam punk aesthetic meant that the plastic gauges with pre-printed backgrounds would not work. Thus it was necessary to disassemble each one and rebuild it in the new case. Avoiding this step and mounting the panel meters intact will save a considerable amount of time.
Other Design Ideas
One idea is to use an economy multi meter, often available for under $10. It would not be difficult to build a small case, add a plug or a cord and an outlet, and wire the system together. This would be considerably simpler and less expensive.
One important consideration is that to measure volatge you must connect the meter across and to measure amperage you must connect it through.
Measuring wattage directly requires expensive laboratory equiptment. Since W = V*A most devices measure voltage and amperage and multply them together. One idea would be to have the needles of a volt meter and ammeter overlap. The wattage could be read at the point where the needles cross.
The simplest answer is simply to have a multiplication chart with the rows being 110, 115, 120, and 125 for the volts and columes of 1-15 for the amps.