There are lots of good guides to making a starter on the forums, and the MrMalty calculator will tell you how big of a starter you need. But for a big lager like a dead guy clone, you will most definitely need a starter.
I usually make a starter 4 days before brew day. In my last 2 batches i collect an extra 2 liters of wort to use as a starter for my next batch. It works really well for me and have noticed a decrease in lag time versus using DME to make a starter.