I haven't done one! I have seen guys lengthen tops after chopping. It is not that hard. The Tex Smith book on chopping is a good one to get. It shows lots of different techniques. If you are not going to shift the top chopping a four door will be very similar to chopping any other top. You just have four doors that need to be fit rather than two.
Check out these links for more info:
http://www.google.com/search?hl=en&q...=Google+Search