I built my window caps using copper sheet and a home made brake. I found the information in an old issue of Fine Homebuilding, you may be able to do a search of back issues. Very nice discussion about how to bend copper, solder it, and form caps for windows and doors. Course if you don't like copper, you could do the same thing with lead, tin or aluminum.
Step one: rent brake and learn how to use it. Step two: learn how to flash an opening properly so that it sheds water outward rather than inward. Many professionals have a difficult time with step two.
Alternatively, you could just hire someone to do that part of the install if you feel comfortable doing the window install (assuming that you are replacing windows, not just wrapping them).
I'd strongly suggest hiring this one out.
Done wrong and it will add to the leaks and look like poop.
Going to need a brake, snips, seamers, a Pea shooter, coil stock nails.
A roll of coil stock, I'd strongly suggest using PVC coil not just painted stock for a longer lasting finish.
What type windows do you have?
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