I'm not going to tell you how to build Riku because I hate that general. I will, however, give you a good process so you can build the deck you want (not just netdeck the typical Riku deck).
When you build an EDH deck, in general, it's good to have an idea of what you want the deck to do. Do you want to combo in everyone's faces? Steal all their s***? Control them until they hate you? Or bludgeon them with unstoppable creatures?
After answering that question for yourself, look at the cards in your colours that do what you want the deck to do. Then look at the ones that are in your budget.
Build the deck and test it out. More often than not, you'll find that the cards you love (for flavor or whatever) aren't as good as you'd hoped. Cut those and replace them with other cards, and try it out. Rinse repeat until you're happy.
EDIT: Also, if you want the deck to do more than one thing, it will help to find creatures/spells that are versatile and that fit into the construction you want.
I basically stole a bunch a list and narrowed down the cards I like but apparently I like way too many.
Anyone have any suggestions of what to cut or cards that I completely overlooked?
Also, this is sort of a medium budget deck (With the exception of the duals that I already have)
Spells
1 Insurrection
1 Devil's Play
1 Genesis Wave
1 Into the Roil
1 Comet Storm
1 Explore
1 Pongify
1 Shattering Pulse
1 Ancient Grudge
1 Hull Breach
1 Capsize
1 Krosan Grip
1 Aftershock
1 Decimate
1 Prophetic Bolt
1 Blasphemous Act
1 Manamorphose
1 Guided Passage
1 Fact or Fiction
1 All Suns' Dawn
1 Hinder
1 Cackling Counterpart
1 Ghostly Flicker
1 Turnabout
1 Plow Under
1 Spitting Image
1 Cultivate
1 Farseek
1 Kodama's Reach
1 Regrowth
1 Beast Within
1 Brainstorm
1 Ponder
1 Worldly Tutor
1 Wild Ricochet
1 Chaos Warp
1 Mystical Tutor
1 Reiterate
1 Rushing River
1 Rite of Replication
Artifacts
1 Lightning Greaves
1 Swiftfoot Boots
1 Relic of Progenitus
1 Rings of Brighthearth
1 Crystal Shard
1 Mimic Vat
1 Darksteel Ingot
1 Mirari
1 Sol Ring
1 Tropical Island
1 Volcanic Island
1 Taiga
1 Hinterland Harbor
1 Sulfur Falls
1 Rootbound Crag
1 Copperline Gorge
1 Simic Growth Chamber
1 Izzet Boilerworks
1 Gruul Turf
1 Mosswort Bridge
1 Spinerock Knoll
1 Alchemist's Refuge
1 Command Tower
1 Lonely Sandbar
1 Reliquary Tower
1 Tranquil Thicket
1 Forgotten Cave
1 Kessig Wolf Run
5 Island
5 Mountain
6 Forest
1 Karplusan Forest
1 Yavimaya Coast
1 Shivan Reef
1 Evolving Wilds
Enchantments
1 Fires of Yavimaya
1 Concordant Crossroads
1 Sylvan Library
1 Rhystic Study
1 Parallel Lives
1 Mystic Remora
Critters
1 Fauna Shaman
1 AEther Adept
1 Man-o'-War
1 Brutalizer Exarch
1 Coiling Oracle
1 Consecrated Sphinx
1 Eternal Witness
1 Izzet Chronarch
1 Kiki-Jiki, Mirror Breaker
1 Mulldrifter
1 Phantasmal Image
1 Phyrexian Metamorph
1 Wort, the Raidmother
1 Yavimaya Elder
1 Primeval Titan
1 Solemn Simulacrum
1 Nephalia Smuggler
1 Bloom Tender
1 Snapcaster Mage
1 Farhaven Elf
1 Fierce Empath
1 Loaming Shaman
1 Pestermite
1 Deceiver Exarch
1 Manic Vandal
1 Flametongue Kavu
1 Oracle of Mul Daya
1 Venser, Shaper Savant
1 Acidic Slime
1 Urabrask the Hidden
1 Warp World
1 Zealous Conscripts
1 Deadeye Navigator
1 Duplicant
1 Avenger of Zendikar
1 Palinchron
1 Sphinx of Uthuun
1 Craterhoof Behemoth
1 Artisan of Kozilek
1 Mindclaw Shaman
1 Wall of Blossoms
1 Seedborn Muse
1 Woodfall Primus
1 Animar, Soul of Elements
1 Nucklavee
1 Thragtusk
1 Mnemonic Wall
When you build an EDH deck, in general, it's good to have an idea of what you want the deck to do. Do you want to combo in everyone's faces? Steal all their s***? Control them until they hate you? Or bludgeon them with unstoppable creatures?
After answering that question for yourself, look at the cards in your colours that do what you want the deck to do. Then look at the ones that are in your budget.
Build the deck and test it out. More often than not, you'll find that the cards you love (for flavor or whatever) aren't as good as you'd hoped. Cut those and replace them with other cards, and try it out. Rinse repeat until you're happy.
EDIT: Also, if you want the deck to do more than one thing, it will help to find creatures/spells that are versatile and that fit into the construction you want.
Thank you to Rivenor for this awesome banner!
Palladia-Mors of {The Spirit of EDH}
EDH
WLinvala, Queen of the AngelsW
WUThe Prison of the Grand ArbiterUW [Primer]
URNiv-Mizzet, Handcycling ComboRU
UTalrand, Drake-Slinging to VictoryU
WUGDerevi, Tactical ShufflingGUW
BCao Cao, Discard Stax of Absolute MiseryB