Warforged, at the moment, are inferior as melee, and this tree does nothing to change that. There are a few gems in it, but overall the tree needs a LOT of work.
The initial one that increases fortification by 50% is fine, as are the ones that increase CON. However, the other ones that increase fortification should be replaced by ones that increase PRR, say by 10 each.
Construct Nature: The repair amp is cool, but as many others have said, it is really only useful for Warforged that can already cast repair spells. At the very least, I would say to increase the repair amp from the enhancement to 10%/20%/30% and the healing amp to 60%/75%/90%. Ideally I would like to see the two separated from each other, with Healer's Friend allowing no penalty to positive energy spells (at the cost of some fortification), and Mechanist as it is.
Construct Toughness: I will be very surprised if anyone takes this enhancement as it is (this extends to every tier so I won't repeat myself). I can see people taking it if 5 HP for 1 AP, but not at the steep price of 5 HP for 2 AP. Just way too expensive.
Construct Nature/Inscribed Armor/Construct Stability: These are fine as they are.
Damage Reduction: 6 AP for 3 damage reduction is a bit steep as it currently is, especially since it can be bypassed by a metal. At the third tier, it should change any amount of DR you have that is /Adamantine to /-.
Great Weapon Aptitude: Terrible in general. Change it to a doublestrike bonus when wielding two-handed weapons (something like 1%/2%/2% for a total of 5% would be great).
Construct Nature/Warforged Tactics: Good
Missing: Give an enhancement line that gives bonuses against poisons and diseases. Tier 1: +3 bonus, Tier 2: +6 bonus, Tier 3: Immunity
Improved Body: My main criticism here is that Composite Body has no bonuses. Give it a dodge bonus maybe?
Brute Fighting: On its own, it is decent. On a Warforged, with lower healing amp, PRR, and survivability than a fleshie in general, it isn't good. Please fix these problems. At the moment, Warforged melee do NOT want lots of threat.
Improved Power Attack: Good
Missing: It would be nice for spellcasters if they could get some benefit here. Perhaps something like, "Improved Inscribed Armor: You have an extra 2/4/6 percent chance to critical with Lightning and Repair spells"?
Warforged Resolve: Terrible. Make it repair (NOT temp HP) equal to the repair skill (not affected by spellpower), and have the +2 bonus to saves apply for 60 seconds.
Weapon Attachment: Awesome.
Finally, have the Warforged body feats be an additional feat at level 1 like the Half-Elf dilettante feats. As it currently stands, taking one of the body feats is spending one of your feats to have inferior armour to a fleshie of an appropriate type. At the very least, it SHOULD be a free feat.