slyder,
roll bar design depends heavily upon the shape of the car. Drawings will only apply if they are of the car you are working on. Soooo, that is to say that there is no place where drawings stored that I know of. Most modeler’s use the roll bars found in pictures of Pro-mod cars and modify the kit structures to match the pictures. I would start there and branch out to full scratchbuilding as your skills grow.
There will be a learning curve, like any other modeling skill, so your first project won't be the best. However, as you work I promise you will get better.
Good Luck!
Also, is that your real name? Could you please put your last name also in the signature text box please? Thank you!
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