Creating a Programmable ROM Logic / Schematic
If the point is to hand-build it, try a diode matrix:

http://www.cca.org/blog/20120222-Diode-Matrix.shtml


  A diode matrix is an extremely low-density form of read-only memory
  that was used in computers in the 50s through the 70s, before EEPROMs
  were invented. (They are actually still used, but only inside
  microchips, not using discrete diodes.) Each bit in the ROM is
  represented by the presence or absence of one diode. The ROM is easily
  user-writable using a soldering iron and pair of wire cutters.