First fixed bike build thread - Help build my first singlespeed or fixed bike

what budget?
You need to figure out what way you go yourself.
If you don't want to have problems with threads then maybe
it would be easier to check classifieds and find something in
your price range.

I need advice on which route people would recommend though, a new singlespeed frame or an older road bike? I'm just not sure. I have done a lot of looking on various forums classifieds and ebay, gumtree etc.

No, but you're asking a broad question which is best answered by browsing through the Current Projects thread or searching "Raleigh", "Peugeot", "first" etc.

In short, no it's not a bad idea at all and from what you write, you are aware of most of the pitfalls (Peugeot seatposts, Raleigh threads etc) and have a good idea of what to look for.

My best advice for a first time builder: "make cheap mistakes".

Yeah, I'll have a look through some more threads, I have looked at quite a few already to find some answers. I think I might go to a few car boot sales to see if I can find any old bikes that are suitable too.