Getting out cards like Myrsmith and Sai, Master Thopterist out early is key to building this artifact powerhouse. Tutoring is important at this point. In fact, the first card you should tutor is one of the following cards;
-Master Transmuter
-Kuldotha Forgemaster
-Darksteel Forge
In reality, all of these should be tutored, but Kuldotha Forgemaster should be the first card you tutor, as it in itself is a tutor card.
After you tutor Kuldotha Forgemaster, the clock starts ticking.
Cast Kuldotha Forgemaster. Next turn, use it's ability and sacrifice three myrs or thopters to put out a Darksteel Forge. Next turn, use Kuldotha Forgemaster again to put out a Master Transmuter. While you could tutor Master Transmuter first, Darksteel Forge will protect artifacts from spot removal (unless it is exile). Now the fun starts. Use Kuldotha Forgemaster to tutor an Ornithopter (if not on the battlefield), then use Master Transmuter to return it to your hand and put out any other artifact card. Now cast Ornithopter out again, creating two thopters (one per Efficient Construction, one for Sai, Master Thopterist), and after paying four colorless mana, copying a Mishra's Self-Replicator (assuming it's on the battlefield), creating a myr (assuming a Myrsmith is on the battlefield), and creating another Ornithopter (assuming a Mirrorworks is on the battlefield). Repeating this over and over again will fill your board with a ton of artifacts.
After you fill your board with artifacts that are hexproof and indestructible, it's time to do some damage. Either cast a Darksteel Juggernaut, use a Master Transmuter (obviously returning an Ornithopter to your hand) to put it on the battlefield, use a Whir of Invention, or use a Kuldotha Forgemaster to tutor it and put it on the battlefield. Darksteel Juggernaut will be massive at this point. Use a Whirler Rogue to make it unblockable and swing for large amounts of damage.
Additional Options:
-Using Tolarian Academy and Hangarback Walker will create a big creature that you can sacrifice using Kuldotha Forgemaster to create a massive amount of thopters. This will also boost Darksteel Juggernaut.
-Using a Bringer of the White Dawn to return artifacts from your graveyard. This is not an artifact and thus will not have hexproof or indestructible. However, running Spellskites will help against spot removal cards unless Padeem is out, then Spellskite is useless.
-Running Orbs of Warding and/or Witchbane Orbs will give you hexproof, preventing instant damage cards from dwindling your life total.
-Running Filigree Angel will cause you to gain massive amounts of life.
-You can use Kuldotha Forgemaster, Master Transmuter, and Mirrorworks on Ancient Dens and Seats of the Synod.