Buy one used, draw the schematic, resell the pedal. Or buy a new one online and then send it back...
Here's a description of the custom shop version. I think it's worth the effort. A useful addition would be a bass cut switch, as in the Boss FA-1.
http://www.in2guitar.com/microamp.html
Please post all the parts values. There are tools to read the codes (electronic assistant 2000 or online).
The try to draw the schematic. Should be easy, you just have to get the orientation of the transistors, diodes, polarized caps and potentiometers right.
Pencil and paper is best for...
An example, two overdrives in on box. In mode A, you can cascade them. In mode B, you can toggle between any of them (and clean bypass) with just one click.
A switching logic for two effects in one enclosure that offers two modes for the footswitches.
A) Each FX has its own bypass switch
B) One switch is master bypass, the other toggles between both effects.
It uses simple spst momentary switches with soft touch instead of expensive and unreliable...