Interesting Frameset under £400 ish

As title, I'm looking for a frameset to build up to teach myself more about the mechanics of the bike. The idea will be to build a nicer bike than my basic trek 1.1 I have now. Don't mind what material but the lighter the better if possible, not the end of the world if it's not though. The only other thing I'd like is something a bit different from the normal bike you see about.
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http://www.ukbikesdepot.com/m90b185s804 ... wgodihIADA
Some frame sets, some frame only for you to spec up with carbon fork.
N+1
From somewhere like Ribble if you don't want to chance one from ebay.
I see Flyxii sell through Amazon now. Not that I know much about them. Any good?
ABCC Cycling Coach
The problem is finding one the right size. Don't compromise on the wrong sized frame for a good price, if you intend to ride the bike much.
The Moser
The VN
Or there are a couple of principia frames at CRC and some more expensive Vitus limited ed ones which look good. I like this one: http://www.chainreactioncycles.com/prin ... prod107243