Hey Holly – there are two main types of radio telescopes: the ones that look like giant satellite dishes, and the ones that look like old-school TV antennas. The second type are really simple and they are literally just made of wire. The dish type used to be made out of sheet metal, but these days we make the dishes out of carbon fibre and coat them with a very thin skin of spray on metal.
Carbon fibre dishes are much much lighter, so we can be more energy efficient in the motors we build to move them to point in different directions.
The reason they need to be coated in spray metal is because the surface has to be a conductor (carbon fibre doesn’t conduct electricity). The wire telescopes are made of metal wires, so they conduct.
If you want to know any more specifics I’m happy to talk about radio telescopes all day… 🙂