This is a shell for 12 Dragon copied from a SCG article on Five-Color Blue Dragons.
The goal is to modify this build to take advantage of the 'if you control a dragon cards' since you have 12, you will statistically almost always have one.
The focus will remain blue most likely, but the mana base may diversify in order to take advantage of those five cards
(Draconic Roar - currently 0, improved Lightning Strike,
Dragonlord's Prerogative - currently 2, improved inspiration,
Foul-Tongue Invocation - currently 0, a staple in Esper sac and gain life,
Orator of Ojutai - currently 0 Improved Wall of Omens,
Silumgar's Scorn - currently 4)

Being a slowish control-ish deck, Draconic Roar may not really be the direction I want to head since the advantage just improves my clock. However, lightning strike is already a great card to slow down aggressive decks, so it may be good.

Dragonlord's Prerogative fights for a slot with Dig Through Time, which have fairly similar effects, but happen at very different times. Prerogative is a true 6 drop, while Dig is often an end of turn three or four drop if you have already hit some decent action. Going more than 2 might be hazardous

Invocation seems like a definite card for slowing down decks by removing something and gaining some life to boot. As mentioned, it is a staple in Esper dragons and considered necessary to make the archetype work, so it seems odd that it is left out of this deck. It also has notable application against decks with few creatures, like Esper dragons or Dimir Control.

Orator of Ojutai is a card I really want to explore, especially for slowing down aggressive decks. In 12Dragon, it is almost sure to draw you a card, so it doesn't matter too much if it only gets a few blocks in. Wall of Omens is good enough to see lots of play in Modern, so I would think that it could certainly fit in Standard if a deck has enough dragons.

This means that the primary changes are likely to revolve around adding some draconic roars (definitely sideboard), invocations (likely split between main and sideboard), and orator of ojutai (which seems good enough to main, but to take out against midrange and control decks). Likely candidates for removal would be encase in ice, voyage's end, nullify, and vault, with nullify and vault being the hardest to remove. No, we really don't care that vault removes our orators since they held off the assault for a while and have already drawn us a card. Every other card is live post-vault activation.

What about Crux of Fate over Perilous Vault?