Yugi's deck revolves around his dark magician's field presence. Unlike in the anime, however, when he gets it on the field, he hasn't got a 100% chance of winning. In real life, your dark magician is likely to be swept off the field by raigeki or something similar. This means a large deck theme must be negation of your opponent's magics, traps and flip effects.
We'll start off by adding some classic M/T staples:
+1 Waboku
+1 Graceful Charity
+1 Harpie's Feather Duster
+1 Raigeki
+1 Mystical Space Typhoon
+1 Pot of Greed
+1 Snatch Steal
+1 Swords of Revealing Light
+1 Monster Reborn
+1 Imperial Order
+1 Call of the Haunted
+1 Magic Cylinder
+1 Dark Hole
Yes, that's a lot of cards, but they're nessecary to keep the deck together. Next, we'll add dark magician and his support cards:
+2 Dark Magician
+2 Dark Magic Curtain
+2 Thousand Knives
This should give dark magician some support and field presence that he desperatly needs as a 7 star monster. We'll also add, to keep to the theme of the deck:
+1 Dark Sage
+1 Time Wizard
Dark Sage himself is actually a useful card. Get him to the graveyard and special summon him for a free magic card. Time Wizard can occasionally help, but is an unreliable way of bringing out Dark Sage. Make sure you have backup if he misfires.
Now, it'd be fine having all these Yugi-style cards, but we do need some 4- star cannon fodder. How about:
+2 Kycoo the Ghost Destroyer
+1 Dark Elf
+2 Gravekeeper's Spy
+1 Gravekeeper's Guard
The Spys can summon each other, allowing for high field presence. Guard's effect cannot nessecarily be used in conjuction with spy's bu he can be brought out as some cannon fodder or with sangan, for a quick fix on an opponent's monster.
Next, we'll add another themed combo:
+1 Magical Hats
+1 Mask of Darkness
+1 Magician of Faith
Magical Hats can, as well as stopping attacks, place Magics or Traps in the graveyard for the other two to add to your hand. This, along with Dark Sage, allows us to search for the exact spells we need. We'll also add:
+1 Sangan
+1 Witch of the Black Forest
+1 Mystic Tomato
For their sheer useful searchability. For some more backup, we'll add
+1 Mystic Plasma Zone
+1 Kuriboh
+1 Book of Moon
And finally, for negating those M/T/Es that'll be targeting our Dark Magician, we'll add:
+1 Solemn Judgement
+1 Seven Tools of the Bandit
+2 Magic Jammer
+1 Royal Command