There's building a rudder blade, the full assembly of blade and rudder head, or everything, including the tiller. Tiller can be made in a number of ways, even adapted from other things like pick-ax handles and what not. I can't speak to that. But I can corroborate that creating a full assembly isn't really all that difficult, and if anything is time consuming at all, it's not the structural parts, but the finishing, that is sanding and painting. In other words, it's like every such project.
The details on my own attempt at rudder building are in the thread
Building a rudder. Not the last word on the subject but perhaps a starting point for improvement.
I've used the rudder since then and it continues to work fine. I enjoy the fact that it floats, in fact, it probably adds almost no net weight at the transom, and the foil shape, while not perfect (nor perfectly executed) is a vast improvement over what was there.
In shaping the foil a power plane and a belt sander definitely speeded up the process, but aren't the only option. In cutting apart rudder head and foil, which I built from the same blank, a jigsaw was handy, but a simple coping saw would be another option. That's it for specialized tools, so it really isn't too complex a job.