Ask Niall! "Niadvice" isn't really that catchy, is it?

I've decided to become a supervillain because of all this roadwork going on outside my house. Do you have any suggestions for a costume?

Yes, but it's really all dependent on what you hope to accomplish. If you want to be a Knight Templar Supervillain, bent on restoring (literal) peace to your neighborhood then I'd suggest white linen, and lots of it. Unfortunately, the obvious choice for a masked, linen costume is taken, so here's something I Google searched:

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OK, so it's not white, but it's beige. That's, like, 10 times better for someone who thinks they're doing good. Beige is like the gun of colours, and when I say gun, I mean it in the Final Fantasy context, being that it's completely harmless (It's a gun, yet it does bugger-all damage! Did you mistake your gunpowder for laundry powder before you went out adventuring? I think you did, ridiculously biologically unproportional character I will conveniently "forget" to Cure out of spite. You would do more damage if you hit the monster with the butt of your gun. You would do more damage if you hit the monster with your unproportional butt!)
That being said, I doubt you're in the right state of mind the purge the world of those you deem to be "evil". No, I suspect you're more in a state of being Driven To Madness, and thus our options can be more suitably extravagant. Let's face it, who doesn't love extravagance? Well, studio accountants coping with the budget for a movie set designed by Wheat, but that's neither here nor there (nor relevant Niall).
Here's my first returned google result suggestion. Take inspiration from male ice skaters. Yes, I know it sounds crazy but, with sensibility and tact, you can find a decent outfit. For instance:

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Classy, scary and will suit most body types. Just get rid of those shoulder... ferrets. Hey, that pose could even be your signature pose (unless you want to be nicknamed "The Lame Seagull", I wouldn't advise it). Just make sure you use your common sense when selecting outfits from ice skaters, lest you end up like Takahiko Kozuka:

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We laugh because it forwards humanity by reminding us not to make the same mistakes as those we laugh at. Collaborative evolution, if you will. So maybe a tight fitting outfit is not your thing? Sure, I have you covered. May I point you toward Coolio, or whatever his name is from Assassin's Creed:

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Intimidating, yet contemporary. I you wear it, the role-reversal from anti-hero to anti-villain is subtle unless some tactless idiot happens to point it out and spoil it for everyone. As a bonus, if you wear this you won't have attention attracted to you as you would with the more traditional outfits.
And, if complexity isn't your thing, you can always stop over-thinking it and go the Classic Man approach:

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Granted, you will have an upper hand if you have a... 1... 2... ...an 18-pack. Is that even physically possible?
Just remember the Golden Rule, conveniently stolen from the only good line in the movie Megamind: The difference between a Villain and a Supervillain...

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...is style.

This is Niall signing off, wishing you a good night and happy advice.