The modern day primitive Flight rules were drafted in the 1980's by Dan Perry and have undergone a several clarifications since. I feel that Dan did an excellent job keeping the rules as simple and consistent as possible and I would suggest using these rules rather than invent something new from scratch. Of course, the organizer of the flight shoot has a lot of discretion. For example, the organizer may choose not to require natural string material, or may not have access to calibrated scales or measuring devices. I wouldn't let those details stand in the way of organizing a flight shoot as long as it is reported when the results are published. The organizers would also have to accept the fact that distances will have an unofficial status if all the standards are not met, but that wouldn't have to stand in the way of having a successful and fun shoot. We are working on a proposal to incorporate these rules into The World Archery organization as well, so the event organizers would have the option to hold record status primitive events world wide.
The basic categories are as follows:
Self bow
35 lb or under (currently youth only), 50 lb or under, Unlimited
Simple Composite (Bows backed with a single lamination)
50-lb or under, Unlimited
Complex Composite - Bows made with any combination of natural materials
50-lb or under, Unlimited
Turkish - Horn, wood, sinew composite shot with a sipur overdraw
No weight class limits
For all the detail, see:
http://www.teamusa.org/USA-Archery/Events/Rules