I'm a casual League player so I'm not that good. I play for fun and not competitive and I'm just sharing this because there is no VI mid build anywhere and because I've had plenty of fun with this build.

Vi is an awesome champ, she can do tons of damage, and wreck any squishy. Yes, she is more effective in the jungle, but this is an alternative, something more fun if you are a VI player and you are tired of jungle. I'm a casual League player so I'm not that good. I play for fun and not competitive and I'm just sharing this because there is no VI mid build anywhere.

Pros

Great CC
Great AD scaling
Natural Tankiness thanks to Passive
Good at catching up with escaping enemies

Cons

Needs Items to do well
If behind, too hard to do well
Sometimes mana hungry

Maw of Malmortius: Best item against AP laner, good Damage and early MR.
The Black Cleaver: Good for tanks when combined with BORK, gives decent Health and Damage.

Trinity Force: VI's Bread and Butter, does TONS OF DAMAGE, with this item by procing SpellBlade passive, gives tons of other good stuff.

Blade of The Ruined King: Great item to win close duels, and for sustain. The active slow is great so enemies can't escape.

Ravenous Hydra: Best item for splitpushing, great sustain and damage.
The Bloodthirster: Great damage and sustain, the shield is also good for Vi.

Ionian Boots of Lucidity: Not much to say. Great CDR.

Mercury's Treads: Good MR,and tenacity.

Ninja Tabi: Good armor, usually take this when behind.

Frozen Mallet: More slow, health and damage.

Spirit Visage: Against AP, great MR, health and regen.

Randuin's Omen: Against AD, great armor, Health and AOE slow.

Banshee's Veil: Against AP bursters and CC.
Guardian Angel: Getting focused? Buy this.