and would it be a good idea to ask to take laying around scrap metal from like construction sites like repairing roads and stuff??
It would be a very BAD idea to take anything from a construction site without asking. And if you asked at one of my sites, I'd be honest and tell you, No, cause I'm scrapping it.

That having been said, I'm constantly amazed at some of the stuff contractors just throw away, as well as what sometimes just shows up in the dumpster over the weekend.