If you want to make your own gears, you might want to look into something called Model Magic. You can find the stuff at AC Moore or Hobby Lobby. It's pretty much bottled liquid foam that hardens into a stiff rubbery texture. I can't vouch for it personally, but I've seen some guys make some pretty impressive Hollow masks from Bleach with it.
Now I've actually done a Steampunk android before, and it didn't take much. A gold plastic mask meant for painting from Micheal's, drywall stilts from ebay, long rubber chemical gloves from ebay, a brown trench coat from goodwill, and some piece of brown burlap to hide the stilts and look like pants. But quite honestly, as striking as it was, I don't think it won anything it I hadn't gotten a group the enter the competition with me.
The question is how elaborate you want to make it. My mask was simple and expressionless, which actually kind of helped the effect. I added goggles only to hide my glasses, and picked those up in the dealter room. One of the guys who entered with me made his mask out of a spraypainted hockey mask, which gave it a lot more of an interesting design.
http://i38.photobucket.com/albums/e136/ ... as_054.jpg(I'm the tall one.) Sorry I can't remember how he did the mouth cover.
There are other things you can toy with too though. Maybe a clear plastic 'window' into your insides revealing just a mess of gears and LEDs. If you want to go with lights too, surf around online for something called "EL sheets/paper/tape". It's really thin sheets of some kind of material that glows like a light bulb, even after it's been cut into whatever shape you want. Personally though, I'd go easy on lights, as it doesn't really fit the genre. Just putting the thought out there.
Cardboard armor or exo-skepeton on the other hand... I haven't tested this myself. But I've heard from a few people that if you soak cardboard in water and form it while it's still soggy, it'll harden in that shape when it drys. Then all you have to do is paint it.
Super Soakers and Nerf guns make excellent Steampunk weapons when painted brass and silver. For an android, I'd recommend something that actually looks like it's attached to you, maybe in place of a hand, or attached to an eyepiece. For part of my costume, I actually have a rig involving dry ice and water to simulate steam. (Make sure to check convention rules on that one if you use that idea.)
You might also consider something that accents the transition between organic and technological. If you've seen Wild Wild West, remember the steampunk cyborg Will Smith faught, and how his face was pretty much just riveted on to a metal skull? Fake tan leather or makeup meant to simulate burns or dead flesh could come in handy there.
Random tubes and pressure meters are always good. I'd hit up the plumbing, gardening, and electrical section of a Home Deopt for inspiration. You can find some flexible metal tubes there that you could just like, wrap around one of your arms.
And to you or anyone else into the genre who'd like to join me in a group entry at next year's cosplay contest, feel free to email me.
kevin_tm@yahoo.com. Hope that helps. Good luck.