I'm building a shed and its 350 feet away from 200 amp service and I want to put in aluminum wire and I need to no what size to use

Is this a new 200 amp service or is it a 200 amp service to your house? What size service are planning to have in your shed?

Using this on line calculator:

Voltage Drop Calculator (http://www.southwire.com/support/voltage-drop-calculator.htm)

Assuming a 40 amp load at 240 volts arrives at:

1 conductor per phase utilizing a #1 Aluminum conductor will limit the voltage drop to 2.83% or less when supplying 40.0 amps for 350 feet on a 240 volt system.