Howdy Bismark9...there are a ton of great aftermarket kits and 3 major PE sets. I have seen some nice out-of-the-box builds, but this is a sweet model, go for the goodies I say. I've just started building mine, head over to my site for a list of major accessories and helpful (hopefully) sources. There are also links to a handful or so of finished boats by various people.
http://www.rocketcopy.biz/models/uboat
Good hunting.
AMP - Accurate Model Parts
Fabric Flags, AM Uboat Goodies & More
http://amp.rokket.biz/