We might also look to the demonflesh golem for inspiration...
A spell with the chaotic or evil descriptor (such as chaos hammer or unholy blight) breaks any slow effect on the golem and cures 1 point of damage for each 3 points of damage it would otherwise deal. It is fully affected by spells with the law or good descriptor, unless its construct traits make it immune to the spell's effects (it cannot be blinded by a holy aura, for example, because that effect allows a Fortitude save).
As an extraplanar creature, a demonflesh golem on the Material Plane can be driven back to its home plane by a dispel evil or dispel chaos spell (as well as by holy word or dictum), but it is not affected by banishment or dismissal since they are not good or lawful spells.
Speaking of extraplanar, I think this should have that subtype and hail from the Abyss. Thoughts?
I think CR 15 is appropriate, actually. Although the drakestone golem has more HD and a better AC, this guy gets more attacks that do more damage, and the poison is in a 100 foot cube, rather than a 30 foot cone of petrification.
You can still make it constructable but difficult. This is a very very powerful golem/creation that would be guarding a main temple and not something easily done. Difficulty would be high, but still plausable. Less construction, crafting it physically, and more a Ritual/Summoning using materials at hand and the golem rises up out of the slab like the T1000 from Terminator 2.
I'm tempted to say it takes a solid block of black marble/ Obsidian /Adamantite sheet of no lesser than 120,000Gold, a gallon of Wyvern's blood (or poison), and a live Octopus.
The octopus must be killed and it's severed head dipped in the bucket and the contents scattered on the slab why casting the spell. Make the spell a Ritual.
CL 14th; Craft Construct, poisonous cloud, x, x, x, caster must be at least 14th level; Price 170,000 gp; Cost 120,000 gp + 7,640 XP
Trying to figure out what other spells you'll need to cast in conjunction to get it to work. This part will take a touch of work.
My suggestion was mostly for NPC bad guys and not for PCs to summon. If they really want to do it I guess they could, but really it's more for flavor text than anything else.
In essence what I described above was a "summoning" of the golem from the parts at hand to "make" this thing come alive. Just throwing some spice at it, if the requirements needs to be more difficult I can go through the SRD and buff the costs and spells associated with it. Heck we can sacrifice a virgin or something on the tablet too!