I am not sure why I would need one.
Unless I thought up something that was actually beyond my infinite capacity in some way. Something that required a universe to provide.
Of course, exceeding your own infinite capacity is trivial, if you are omnipotent. Perhaps it would be something inherently unachievable by self. Something that I could not do, without creating a paradox.
But, I have no idea what it would be.
Tris
Two words: Magnetic monopoles.
I would probably design the universe to be even cooler (figuratively that is, 2.3K is cool enough) than it is now, throw in stuff like practical intergalactic travel, and make human society more utopic. Then I would make myself a human without any memory of my god status so I could enjoy my work. After all, you don’t invent baseball so that you can be the umpire, you invent it to play it. But when I died I would go back to being god again. But I might give myself some cool superhuman powers like telekinesis or extraordinary luck to make my stay a even more enjoyable.
I am a god(dess) - I play Black & White.
It can be a lonely world without pets.
I’d create one without the second law of thermodynamics. 
Spoken like a true Borgia.
I’d make assholes reincarnate as some hideous thing, like an orb web spider or and earwig, but with their memories, aspirations and self-awareness they had when they were human intact. Any attempt to communicate with the human population, I would make futile. They’d still have the in-borne instincts of said creature, but would still be repulsed by it, and would yearn for their human comforts and food. AHH HA! Take that Mike Greene from the 8th grade! Asshole.
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We’re trying to think up something different from the universe as it is now, Larry.
Ditto, but if I had to I’d create one exactly like this one. The plans have to be in the public domain by now, unless Disney has managed to convince Congress to retroactively extend copyrights back to the Big Bang, which I don’t think they have, yet.
See end of post #9.
moo
I mean, purrrrrrrr
Well, reality would just be a big computer game, so it would be just like it is, except that this world would be only one level for myself (and any other spirits/ghosts/gods that happen to be around) to play in. There would also be a Star Trek one, and one where ESP and stuff actually works, ones set at various interesting points in history, ones where you can reincarnate your characters back at the last save point or nearest town (unlike this ‘Hardcore’ reality we live in), ones where you play as an overarching diety and other ones where you play as just another of the peons, ones with dragons and magic, ones where everyone has horns on their head, and anything else I could think of.
I’d make new universes all the time, moving from one to the other as I see fit, to keep myself and my godly friends (I’d make some if I need 'em) entertained. When I got tired of playing in one universe I’d leave it to run in my absence, maybe coming back, maybe not, since, of course, none of the little video game character people matter to me. Except when I’m actually playing, in which case my mario is totally awesome, and my chosen people are going to come into your promised land and knock your city walls, and they’d better be doing any silly thing I tell them to.
Yea…but that’s why you are trapped where you are…staring out at the universe using a bowl.
And it would eat villagers**, an interesting role reversal…
My universe would be very much like the Sims 2, in that it’d have Aliens***, Zombies, Vampires, Werewolves, Robots, and Plant-based humanoids, as well as Cowplants
Interstellar travel would be common and almost mundane, teleporters would exist too
**that is, when it wasn’t sitting on them or throwing them around, Obey the CowGod!
***lets see, there’d be Klingons, Vulcans, Cardassians, Ferengi, all the Trek races except the Borg, as well as Cylons (TOS Centurions, new Centurions, Meatbags and the like), Nebari, Delvians, Sebeceans, Scarrans, Luxans, Hynerians, Tavloids, whatever species Pilot is, Leviathans, etc…, you name it, if it’s a sentient alien race, it exists
Oh, and all religion would be outlawed, any lifeform doing things “in my name” would recieve a free, no added expense, limit one per customer, Wipe-and-Restore of that section of their brain
The most bizzarre, impossible, un-credible Universe possible. So much so that when the vast seas of Intelligent creatures arose therein, they would have no ultimate choice but to admit that there had to be a God, an ultimate creator, and that he (me) was deliberately jerking their chains. 
Like an entire planet where the continents spelled out my name. Arrows of stars in space, pointing to Really Cool Things. Highly Improbable rescues from celestial events (like a previously unknown massive rogue planet just happening to eclipse a planet just before it gets hit with a gamma burst from a nearby supernova strong enough to sterilize it.) Moons made of obscure cheeses. Planet Nerf.
Should I decide to provide a personal afterlife, it will have a lot more in common with Islamic Paradise than Christian Heaven. There will be no Hell; souls I deem unworthy will be rendered unconscious and placed in storage indefinitely or until I can think of a use for them.
Should I decide to go with reincarnation, it will not involve any element of karma. Humans will be reincarnated as humans, but otherwise the process will be entirely random – you might be reborn a human of any nation, race, gender, class, or circumstances. I will make sure this is widely and indisputably known; if you want a better life next time around, the only thing you can do about that is spend this life making the world as a whole better for everybody.
When I was 10 I went out to the stream behind my grand parents yard and built a small island with mud and rocks and populated it with red ants I captured in a jar. Then I got bored and threw rocks at it.
I don’t think 19 years has changed me much.
In *my * universe, testicles are on the inside.