Best armor enhancements for a dragon

[Darkon47]

I am currently stating out a major boss for my 3.P game, there was a sudden turn towards the unexpected at the end, and I now find myself having to gear up Tiamat's main squeeze, I am pretty well set in terms of most of their gear (for a half fiend great wyrm red dragon) But I find myself struggling on their last armor enhancements, their armor is currently +5 heavy fortification, but it has a level 6 fiend of possession in it, and I find myself unsure of what to do for the last +6 of enhancements, I think I may need to increase the hardness farther (it will need to endure 1d6+30 fire damage and an equal amount of unholy damage every round)

I know of the weapon enhancement handbook, but if anyone can link to a similar one for armor enhancements that would be great, barring that any suggestions would be great!

[DrMotives]

Since red dragons have a cold weakness, some cold resistance would be fitting on armor worn by one. Shoring up the obvious weak points is pretty basic planning.

[Crake]

Where's this fire and unholy damage originating from? Attended objects aren't typically subject to effects that affect creatures, so unless otherwise specified, the gear should be alright.

That said, since you're using a fiend of possession, which can change the properties of your armor as a standard action each round (unless otherwise noted, using an Su ability, like the fiend of possession's magic item ability, is a standard action), having a set bonus is actually less useful. Instead have the fiend constantly adapt the armor to provide relevant bonuses, perhaps even readying it's action to resist attacks as they come.

[Blackhawk748]

I'd second the Frost Resist, hell toss the other 2 elements on as well. May as well make the giant meatwall even more durable.

[Darrin]

Check out the 3.5 Armor and Shield thread (http://www.giantitp.com/forums/showthread.php?445923-Saving-from-WOTC-Forum-The-3-5-Armor-and-Shield-thread).

I also catalogued all the various armor enhancements (posted in that thread), and I noticed that most of them aren't worth the bother... they usually trade a +1 AC all-the-time bonus for some other bonus that only applies in certain situations. So it's almost always a trade-down in terms of utility. There's only a handful of armor enhancements that are "worth it": a few +1 abilities, and a few +4/+5 abilities, but hardly anything in-between. I generally start with Death Ward at +1, Fortification at +1, upgrade to Moderate Fortification at +3, Soulfire at +4, and Freedom at +5.

If you've got +6 to fill out, I'd say Death Ward + Freedom should do it.

[Eldariel]

If you want to shift some value into flat enhancements, I like the flat price (Greater) Healing [MIC] to combine with contingent Revivify. Automatic return to consciousness off the healing is very convenient. Fearsome [Drow of the Underdark] is very strong particularly with Imperious Command.

Far as plusses go, Soulfire [BoED] at +4 is also nice as a permanentish negative energy protection.

[CharonsHelper]

Make sure it's adamantine. The dragon likely gains nothing from mithril and the cost is insignificant by that level.

The bigger thing to decide than armor are the dragon's buffs. It can cast as a really high level sorcerer so it should have long-term buffs up all of the time and likely some shorter buffs on contingency so that it doesn't have to spend actions casting them.

[Eldariel]

Make sure it's adamantine. The dragon likely gains nothing from mithril and the cost is insignificant by that level.

Well, Oerthblood [DR351] is strictly better if available.