I just built one actually. I found the schematic and sound clip on
http://www.runoffgroove.com. The project is called the Little Gem. No kit though - I just bought the parts I needed and threw it together. It is very simple, inexpensive and easy to build, and the sound is pretty cool for clean to gritty. No high gain available though - you'll need a pedal for that. Listen to the clip and see if you like it. Mine came out sounding pretty similar, although I play it through a 1x12 open back, so I don't get the same bottom that the clip exhibits (he used a 2x12 closed back probably).