There are lots of overdrives I like and enjoy, but I keep coming back to the Boss OD-3. BYOC already offers the "parent" of the OD-3, the
Blue Overdrive (BD-2 clone). My understanding is the OD-3 is essentially an evolution of some of the design ideas in the BD-2. To my knowledge, the topology of the BD-2 and OD-3 are fairly unique in the crowded overdrive stompbox world (specifically, the use of differentials or essentially discrete op-amps).
I actually thought to do this myself, as the OD-3 schematic is readily available on the web. The problem I ran into is that all the transistors used in the OD-3 are not readily available, current production parts. I started to search for equivalent parts, but wasn't able to find obvious drop-in replacements. So I think the challenge is for someone with actual circuit building experience to figure out what characteristics are most important for the transistors used in the OD-3 circuit, and find acceptable substitutes. Depending on what's available, I suspect other parts of the circuit may need to be tweaked to accommodate the replacement components.
I personally think the OD-3 is nearly perfect, though there I times I think a bass trim pot would be nice (like the Timmy, or Aion's Nobels ODR-1 clone).
Anyway, just throwing it out there!