I followed the guide above for about 5 matches and I was never getting ruins, just artifacts. Then I remembered I was playing some matches before that featured ruins, which were set on the INLAND type of map.
Basically what I did was quit and set a match with the following settings:
Game Mode: Random Map
Map Type: Inland
Map Size: Medium
Reveal Map: All Visible
Speed: Very Fast
The rest of the options choose as you please, it really doesn't matter.
And BOOM! there are the ruins. As stated on the guide above, spawn cars using the 'bigdaddy' console command and send 1 or 2 to each ruin to hold them off (there are about 4-5). When you see a time counter appear on the upper right corner as "Ruins: (year)" then the countdown has begun for your victory and now you just have to remain there until it finishes. You can set the diplomacy with you 2nd player to Ally and that helps as well so you don't get randomly attacked.