You shall not pass!

I've fallen in love with Vulcan since I first took him to a test run. I've been playing Vulcan more or less since he was first released and in various forms. Since I first played him as a tank, I kind of still got the habit on building him more on holding the lane and consistent damage rather than glass-cannonish burst. So this guide will be an alternative for him. The build I at least personally prefer and in my opinion works better.

The key factor which people tend to forget is to prioritize Inferno Cannon over Magma Bomb.
Simply the fact that Magma Bomb, even with CDR capped, has just way too long CDR.
I use Magma Bomb just to poke and feed my enemies to my long love, the almighty Inferno Cannon. Combining the 2 skills gives you some serious zoning capabilities. Also you need 1 point in Backfire for escapes/tagging people. With CDR maxed, don't be afraid to use your ulti just for zoning since the CD will be rather quick. Can't compare to Ra or Anubis of course, but still.

Key to the consistent damage stand mainly behind cooldown reduction. The first item for me is more or less always Chronos' Pendant.
The next in line is rather a personal preference with the boots, I personally like to go all out on cooldown rating.
Now we start forward on staying in the lane and go with Warlocks Sash and Ethereal Staff This will simultaneously increase your damage output and survivability, resulting in 3000 HP with full stacks at level 20.
Now to make your attack even more, we'll go with Obsidian Shard.
And of course, as a cherry on top as with all mages, Rod of Tahuti.

It's a matter of personal preferences really.
I usually go with Meditation/Aegis combo.
Meditation simpy for more constant nuking and staying in the lane which later on gives you also some healing for those sticky situations.
About Aegis.. Well, the reasons are quite obvious.

I see a lot of people build lifesteal items on Vulcan, which in my opinion is rather useless. The main reason being that your primary damage output is from your turret skill, simply because magma bomb cooldown is way too long to be beneficial and lifesteal DOES NOT transfer over to turret hits. The other reason would be for items like Talon the magical power output, but then again, since Vulcan is a type of mage that's nearly always close to the action and WILL be focused whenever possible (simply because turrets piss people off), you won't be enjoying the full benefits of the lower-hp-higher-damage bonuses and will be sitting and waiting to respawn.

The only lifesteal item, which could be used as a situational item, for example Assault game mode, would be in my opinion Divine Ruin. And that for it's passive rather than it's lifesteal capabilities.

The tradeoff in damage is not that much of a loss, if not added special passives like for example the one from Soul Reaver. From your ultimate if I recall you drop around 200-300 damage, while it already is one of the hardest hitting abilities in the game.

While you might think, the more damage, the better. Well, actually no, if you come to lane just to land a few skills and be taken out by the enemy assassin, you're hardly any use to your team. In trade off to lose that bit of damage, you basicly double your surviving capabilities.

Vulcan who stays in the lane, nearly always wins the lane.

The main thing is to remember not to be afraid to use your turret even just as cannon fodder. As a mage you have above average mana pool and your turret can outstand a couple of skills. So it could be wise to just leave your turret as a cannonfodder, zoning your enemies. Then they have 2 options to advance against a well positioned turret. - Either move in to attack it with basic attacks and lose a bit of health or use your long-range skills to take it out, witch ticks away their mana and is one step closer to force them out of the lane.

The arch-nemesis for all mages is those pesky little assassins. With this build and little practice you can win a duel against most of the assassins instead of trying to run away from them and still dying due to lack of escape skills.
The key to fighting someone alone is actually rather simple, instead of moving away from them, you have to act against logic and stick to them, keep them in front of the turret and control them. Most of the assassins are used to taking squishy mages out without an effort and don't really expect you to actually fight back. The tactics would be to stay in the turret range, whenever they get to you, backfire away, tagging them and landing some extra damage and/or magmabomb the ground you stand on, throwing them further. Also if you have ultimate available, don't be afraid to use it due to it's rather low CDR. This will give them 2 options - Either try to run and leave you alone or stay and take it, with usually assassins not building any defence and rather low HP pool, they usually lose nearly half of their HP from your ulti alone.