Would like to find out the specs to build a box for 2 12inch mtx Thunder 9500 serious for a 1996 dodge ram 1500 I be running a boss amp 5000watt 1000 RMS single channel amp
There are no set in stone specs. You'll need to know the T/S parameters of the driver and then decide what type of enclosure you want to build. Most automotive subs are placed in vented enclosures but they require more math and a bit more work than a simple sealed box.
Probably the driver manufacturer has enclosure suggestions on their web site or, if you contact them directly, they can direct you to another webpage for ideas.
Offhand, I'd say you aren't starting off well. You bought a driver without a clue as to how to build the box and you posted a car audio question in the home audio forum