putting 12 ldr on my arduino uno board

Using Arduino Sensors
3

You can multiplex the LDR's quite easily with - SparkFun Analog/Digital MUX Breakout - CD74HC4067 - BOB-09056 - SparkFun Electronics? - you can address the board with 4 digital lines to select one of the 12 LDR's

select LDR 0 all lines are LOW -

A function like this can be handy to set the right lines HIGH/LOW

int readLDR(uint8_t nr)
{
  digitalWrite(..., nr & 1);
  digitalWrite(..., nr & 2);
  digitalWrite(..., nr & 4);
  digitalWrite(..., nr & 8);
  analogRead(A0);  // to prevent a bit of noise
  return analogRead(A0);
}