h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I'm cleaning up and refurbishing a crystal radio for a friend. It requires an aerial. There's lots on info on the net regarding length and position of aerials but no mention of their construction. What gauge wire? Material (copper I guess)? Should it be insulated or bare? Where would I be able to buy such wire? At the end of the war my parents were able to buy a Ferranti valve radio and I remember a long wire aerial being hung up to the rooftop and local experts giving advice on the positioning. The aerial was bought from a local shop which sold valves and recharged accumulators. The shop has, of course, gone, aye ages long ago. The local Tandy shop has gone too, though there is a Maplins in the nearest city. I would be grateful for any observations on this vexing subject.
Regards
202634 (is that an acceptable format, or do I resuscitate my schooldays nickname?)