p=0;
for( x = 0; x < gridMax; x++ ){
  for( y = 0; y < gridMax; y++ ){
    if(x+1 < gridMax && grid[x,y].RoomHere != grid[x+1,y].RoomHere) p++;
    if(y+1 < gridMax && grid[x,y].RoomHere != grid[x,y+1].RoomHere) p++;
  }
}

//p holds the perimeter