Most Popular
If you want to use the most popular Mel Mid build, you should take Flash and Teleport as your Summoner Spells. For runes, you should pick Arcane Comet as your keystone, followed by Manaflow Band, Transcendence and Scorch in the primary tree, as well as Presence of Mind and Coup de Grace in the secondary tree. For rune shards, you want Ability Haste in offense, Adaptive Force in flex and Health Scaling in defense, though it depends on the matchup. Finally, for your items, you should build Luden's Companion as your first item, followed by Sorcerer's Shoes and Shadowflame. For your last 3 items, you should build Rabadon's Deathcap, Void Staff and finish with Zhonya's Hourglass. For the skill order, you want to stick with Q - E - W. Right now, this build has 49.1% winrate over 2 007 matches played.

Optional
Your second option for Mel Mid build would be to take Flash and Teleport as your Summoner Spells. The runes that this build takes advantage of are Arcane Comet as your keystone, Manaflow Band, Transcendence and Scorch in the primary tree, and Presence of Mind with Coup de Grace in the secondary tree. The shards used in this build are Ability Haste in offense, Adaptive Force in flex and Health Scaling in defense. The items for the build are Archangel's Staff, which you should build first, followed by Sorcerer's Shoes as your second item and Liandry's Torment as your third item. The rest of the items in order are Cosmic Drive, Rabadon's Deathcap and Void Staff. The skill order for this build is Q - E - W. In the current patch, this build has a 51.5% win rate over 408 matches.

Alternative
If you're looking for alternatives, you can use Flash and Teleport as your Summoner Spells, with runes being Arcane Comet as your keystone, Manaflow Band, Transcendence and Scorch in the primary tree, and Presence of Mind with Coup de Grace in the secondary tree, as well as Ability Haste, Adaptive Force, and Health Scaling as your rune shards. The items that this build incorporates are Blackfire Torch as your first item, then Sorcerer's Shoes as a second item and Liandry's Torment as a third item. You want to finish the build with Shadowflame, Rabadon's Deathcap and Void Staff. As far as ability max order goes, you want to keep it Q - E - W. This build is currently sitting at a 52.0% win rate across 333 matches played.

Off-Meta
If you want to try an Off-Meta Mel Mid build in the current patch, try Flash and Teleport as your Summoner Spells, Dark Harvest, Cheap Shot, Sixth Sense and Ultimate Hunter as your primary rune tree, and Manaflow Band with Scorch as your secondary tree. Use Adaptive Force, Adaptive Force and Health as your shards. For items in this build, you want to complete Luden's Companion as your first item, then finish Sorcerer's Shoes as your second item, and Shadowflame as third item. The last 3 options are Rabadon's Deathcap, Void Staff and Banshee's Veil. The ability order for this build is Q - E - W. As of the current patch, this build has a 48.3% win rate over 205 matches played.

Situational Mel Runes and Items
Depending on the context of your game, your matchup, and enemy champions, you might want to consider building some situational items or take specific runes. Carefully examine your team, enemy team, game state , and your matchup to plan your Mel build accordingly! For example, when it comes to rune shards, you might want to take either Armor or Magic Resist, depending on which champion you are about to lane against.