What type/gauge wire do I need to run 200 feet from transformer to meter for 100 amp service in an out building? Is 2 inch conduit sufficiant?
If it were feeder, you'd be required to use 1 AWG aluminum. Since you say it is a service lateral, you would be allowed to use wire sufficient for only 83% of 100 amp, or 2 AWG Al. However, given the distance involved you're probably going to want to upgrade to 1 AWG aluminum to avoid too much voltage drop.
As far as copper, you can use it if money is No Object, however normally this big stuff is aluminum and it works perfectly fine. The attachment lugs will be aluminum, so that keeps the metals the same.
You might squeeze that into 2 inch conduit if you know enough swear words! However, as a DIY person, I would much rather be pulling it through 3 inch conduit.