Want advice on Building a computer.

Can anyone give general advice (this is for my Dad) as he wants to build our first computer. Perhaps you know of some good sites (we live in the UK) that are recommendable for parts. (Maybe ebay).
Which parts are best bought new, which are ok second hand etc. He is a lot better on computers than me
but we'd like to do it - it's just that we haven't done anything like it before apart from the usual fittings on upgrades.
Maybe someone could match up a selection of bits from a British site that we need. Price tag is roughly
Which parts are best bought new, which are ok second hand etc. He is a lot better on computers than me

Maybe someone could match up a selection of bits from a British site that we need. Price tag is roughly