After decided the measurement of the tables, it is easier to plan the layout. Then, I put all the 20 computers in the shop plan. Try to find the best layout. After a few change here and there, finally I found that the layout as you can see from the images below, which is the best of I can think. Of course, this is just my opinion.
After we finalizing the layout, then it time to think about the electrical wiring.
Electrical wiring works should be done by licensed contractor, but you should know what the contractor have to do, such as how many sockets you want and where are they placed.
There should be a sufficient number of socket outlets in the internet cafe area for all your needs. For safety and for your own convenient, it is best to have 2 electric sockets for each computer. One for the CPU and another is for the monitor. For the speakers, USB powered speakers should be used.
But because of the high cost you might want to have just one electric socket for each computer. Make sure your computers’ power supply have power output for the monitor. In the future, when you have to replace the power supply, make sure you buy the right one, which have power output for the monitor.
Another thing to consider is electric sockets placement. It might be dangerous to place the socket too low from the floor. It is dangerous for the customer and it is not so convenience. I think the best practice is to put the socket at the same height of the computer monitor and make sure it is placed behind the monitor.
If the computers are far away from the wall, consider to use a high quality extension socket. And for your properties and your own safety, do not connect multiple appliances to a single socket with a simple double adaptor or block socket adaptor. If necessary, use a multi-outlet safety plug board that has a built-in overload cutout feature.
Beside electric socket for the computers, there should be sockets for modem, switch, printer, scanner etc.