Should never have any guilt at all building something for yourself. As long as you aren't selling them to anyone, go nuts, you aren't infringing on anyone's IP or breaking any law. This really is the best way to go for most of the basic stuff: buffers, loop switchers, fuzz pedals, that sort of thing. You can build with a better quality enclosure, jacks, switches, etc to get a more robust pedal in the end, and usually wind up paying around the same amount as an "original". Except now you can back a truck over it and it will keep on working. And you built it so if it fails in some way, you know how to fix it instead of tossing it.
