The make of wire isn't hugely important. Just use stranded copper wire as it is easier to work with. The biggest thing is the connectors, 90% of the time if you have a wiring issue it is the connector, or really close to it. Solider all the connections and make sure you use heat shrink, I like the type with glue inside. When it heat it up the shirk gets tight and the glue seals everything.
A 12 Gauge wire is good for up to about 100W on 12V. Since the bird only has about 100-150W of extra power it should be fine to run most everything on 12Gauge wire. The main wire from battery to Aux fuse block you might want to use 8 or 10G if you have allot of electrical accessories.
The following site lists rating for wire size.
http://www.powerstream.com/Wire_Size.htm