I looked up the wire size in my electrical engineering reference and it shows that 2/0 type THHN copper with the ambient temperature for the hot summer weather factored in has an ampacity of 170 amps. Service entrances require the summertime ambient temperature be factored in to allow for the hot weather because these wires are directly exposed to the weather so you will need 3/0 type THHN copper wire only. Do not use aluminum wire and be absloutely sure to apply antioxidant compound to ALL connections. Minimum conduit size you will need is 2 inch conduit.
Your 200 AMP service will need 2/0 for hot wires, 1/0 for neutral and #6 for your 4th wire when working with copper. If you are using aluminum you will need 4/0 for hot on a 200 amp service, 2/0 for neutral and #4 for your 4th wire. The 4th wire can also be sub-pane and MH. Your local county should be able to tell you what the codes are that are required for your area.