"One of those pieces" is poorly defined. Describe the piece, or check out these pages:
http://paragonwiki.com/wiki/Unlockable_Costume_Pieces
http://paragonwiki.com/wiki/Super_Booster_I:_Cyborg
Yeah, the cyborg booster pack is pretty good for robots. If you don't have the cash to spring for it though, I suggest you try mixing 'Enforcer' details with robotic face textures; that might work for you.
"If I had Force powers, vacuum or not my cape/clothes/hair would always be blowing in the Dramatic Wind." - Tenzhi
Characters
Female Transformer
I modeled it on the old version of Arcee in an attempt to get the 'old cartoon' feel you wanted.
Also, no knowing what bits/pieces you had access to I stuck with just normal bits from the costume creator. And as for the face, I'd say that the most attractive robot/technological face for females is Metallic, which is the face I used.
Hope this helps! 
- El D
Global - @El D
Servers - Protector
I pretty much have every costume pack piece.. just no idea on what unlockable ones (from TFs and whatnot) are better suited.. I really want to say the valkary faceplate is what i saw but it doesn't look like it... unfortuantly I don't have the vet reward for that anime style armor.. so i don't know if thats what I'm looking for.
EDITX2!!
I will note that the website does NOT show all the roman armor options, despite listing several for the same slot.
Very nice take on Arcee though!
Tech Sleek? Don't recall any helmet/face options there. :/ But, there are some definately interesting armor bits. IIRC, male pictured there has the majority of the pieces on.
I'd link some of my robotic types... but I extensively abuse the Cyborg 2 (the face shield bit) detail for it. :/ I'm a sucker for headgear.
As the title says.. I need help making a costume.. specificly I need help making an attractive head for my Female Robot.. but all I come up with look like total slag... part of what I'm trying to do involves making the head resemble the bots from the transformers series.. ((Not the movie or the newer cartoon.. the older cartoons.))
Any idea on what I could do? I've seen a few odd pieces that aren't immeadiatly available to me that would otherwise help.. but I don't know where to get them... so if you're using one of those pieces.. please let me know how I can obtain it.