What can I used to weight down my house flags, garden flags. They are hanging from the eves and keep blowing up over the roof.?

You can try to sew back just enough to stick a rod thru, or sew little magnets or weights into the two bottom corners. 

Or hang something more weighty from the bottom of the flag, but that could be dangerous in high winds, if it whips around....or crack a window if it's too close. 

Gorilla Glue them to the eves. Problem solved.

Metal rod sown into the bottom hem.