No problem. I tried two ways and both worked well.
1. Using flat bar aluminum. I cut it to size and then measure where I want the angles to be. I used my drill press to drill holes in it before bending. Then I use my bench vise to hold it in place to hammer it to a 90-degree angle. ***depending on the thickness I use a little blow torch to heat the metal just at the angle.
2. Instead of buying flat bar aluminum, just by the lumber ties in the lumber section of Home Depot. They are usually thinner, have multiple sizes, and have the holes pre-drilled. Cut it to size and repeat the steps above but without the torch.