The way I play I enjoy a lot. It's a tank-support build. The general idea is to fill any gaps in a team. I was replying to the identity crisis thread and I figured the post would be long enough to make a guide.

It's fairly different to the other ways I've seen Engi played and none of the guides I've found give the same instructions. Feedback is always welcome.

The skill build goes:
Level 1: Turret 1
Level 2: Keg 1
Level 3: Tinker 1
Level 4: Tinker 2
Level 5: Tinker 3
Level 6: Ult
Level 7: Tinker 4

After that, Stats/Keg depending on how much mana is going around.

Turret serves as a free rune/forest gap ward. Always placed on the hill which will give it LOS to either the rune or the ramp into your team's forest. Put it on hold or run it out of mana to prevent it shooting and giving itself away.

More points go into Turret only later once the DPS is actually worth feeding the enemy ~70 gold and destroying your "free ward". Probably around level 16/17 if making the late DPS items, otherwise never putting another point into it until Stats is full.

The reasons behind maxing Tinker instead of putting points into Keg are:
- Keg becomes very expensive fast if you level it too quickly. Engi will suffer early mana problems with Kegs costing too much.
- Level 1 Keg + Level 4 Tinker = Kegs costing 58 mana. Because neither the range nor the knockback distance scale with the level, it's an excellent skill when it's kept so cheap.
- Tinker is a superior skill overall. Level 4 Tinker early in the game is awesome for pushing enemy towers and for totally derailing early enemy pushes. As Engi I've single-handedly prevented an early 4v1 push while our team pushes 2 lanes by dropping my Ult, tinkering our tower and running away.

Early items:
- Bottle if mid. If I'm mid also 1 point in Turret gives me a free ward.
- Bracer for early HP and to compensate for the lack of Steamboots
- Phase Boots for max. speed/gold and extra damage
- Tablet of Command for fun - it's extremely versatile - getaways, chasing for me and my allies. Forcing an enemy hero out of position. Mainly with Engi though is skipping people through the walls of my ulti.
- Then a HotBL, to prevent me being instagibbed when I initiate with my ult, and so I can totally rape towers solo. Level 4 Tinker + Helm = towers tickle.

Then it depends entirely on who's in the game, he can fill any role he wants late game:
- Pkey to combine with any of our team's AOE initiations [slap it around Tempest/Behe/SS whatever to prevent escapee] if we need stronger initiations.
- Shroud if they have no Pest/Arach types AND we don't have any invis heroes already, for even better getaways and initiations, and for the attack bonuses later on if I need to help late DPS.
- Barrier Idol to counter something like or
- Astrolabe if we lack healers
- Puzzlebox if they have invis [this works very nicely in the ult]
- Riftshards/Shieldbreaker if we lack late game DPS

I might update this with more protips. Right now I'm tired.