Thinking of my first build... Advice?

Cannondales are you friend if you want gears.
If you are looking for fixed gear (I presume) then have a look at meilec bikes, they are awesome and very cheap for a bespoke Alu frame. With forks may cost a little more than £200 but its a worthy compromise.
http://www.bikemielec.com/en/ostre_kolo_szosa.php
Or something like a Dolan pre cursa/ track champ if you don't care about snobbery.

Thanks, Loctez. Will be building a fixed gear, yeah. Circa £200+ with forks is very reasonable.

Apologies for the vague OP, but I'm still new at this haha.