I know mostly where to look, but I wasn't having too much luck. I think it's too specific.. I'd like to make a tremolo that has selectable waveform and an expression pedal to control the speed. I think the expression part might be a little specific. Perhaps if someone can point me in the direction of the tremolo and someone to a how-to-guide of adding and expression in.
Check Generalguitargadgets.com they have schematics or search for Aron's DIY pedal forum or the Indy guitarist forum. They'll help you out.

The Expression pedal is something you could add to any existing schematic so you might as well just find a trem that you like and add the pedal to it.