Double rods: You will need to purchase two size rods that are the same in finish: a larger one for the front rod and a smaller one for the back sheer rod. Install the larger rod first and then just on the inside of that bracket, install the smaller rod’s bracket.
My double industrial conduit curtain rod. I made this with pipe fitting and electrical conduit. Pipe fittings cost $15.00, conduit and spray paint cost $13.00. Cost per window is about $28.00 in Oregon where we have no sales tax.
DIY curtain rods: 2 or 3 of this style hook ($1.99 each at Hobby Lobby.) If your rod is over 6 ft, you’ll need 3 of them to support the extra weight. Plus a piece of closet rod from the hardware store cut to the length you need the rod (mine was about $10 for 11 ft. – because it’s sold by the foot, they’ll cut it for you), plus a pair of wooden finials (I found mine at Hobby Lobby for $3 for the pair.)