Choosing Reflector material

I don't know the effect of material constructing metal reflector it could make from:
- copper
- aluminum
- Steel
- Iron

I don't want to mention on mechanical characteristic. What kind of material should use?

For UHF to microwave region, any of metals you listed can be used. Corrosion can be prevented by paint or varnish.
Metal conductivity starts being important approx.above 100 GHz.
You can even try carbon-fiber composite board as a reflector, it works fine at ~10 GHz even having ~100 Ohms/square.

It depends. Reflection as better as better conductivity. The best are superconductors (they works with low temperature and it is somewhere from fundamental physics and some space applications BPFs and Duplexers ) then silver, cooper, aluminum and so on. But practically all metals works well and not only. For instance I watched birds eagles on the radar screen with distances up to hungered kilometers.
http://www.hope.edu/academic/physics...Supercond.html