Stock fenders are just metal with a chrome finish. You can reshape by cutting, grinding, hammering, plasma cutting (even biting) them. Some builders fab cardboard into shapes as a mock-up to get it looking just right. The they transfer the shape to the fender with a magic marker and start removing metal.
If you intend to paint you parts, once you have a finished form, use high quality sand paper on an orbital sander to get a smooth,consistent finish on you fenders. The chrome does not need to be completely removed, just roughed up. Also might consider using body filler to smooth out the odd dings. Then you prime it and paint it to your satisfaction.
I look forward to you progress.