There are no real rules to this. I have seen long flag poles, and I have seen short. We use a broomstick length of carbon fiber for our flag poles.
Your flag should have your team number or logo on it and you bring it to the field with you when you play. They usually have someone helping coordinate that so the MC knows whose flag is whose.
Try to keep the pole light but strong enough to not break. A 4.5 to 6 ft. Pole would be about right.
Have your technician ready to take the flag and return it to your cart.
Place the flag unrolled on the charge station with the holding end pointing to mid field. Lined up with your drivers position.
PVC flagpoles work well, and might be a tad friendlier in terms of budget. Feel free to paint it or wrap it in your favorite color tape.
If you do make a flag, I would also recommend making a flag holder on your robot cart so that the drive team members don’t have to carry it around everywhere. Plus it helps keep the flag clean since it would likely end up lying on the floor otherwise!
PVC, carbon fiber, anything like that will work fine.
Something that the NE district did for their division flags this year was they gaff taped it to a broom handle and that worked fine, so you could try one of those as well.
Some may think Scott is joking here, but it’s a serious and great answer (especially for us Canadian’s).
2386 used to frequently attend regionals in the US, and we’d regularly bring a Canadian flag mounted to a hockey stick as our “team flag”. It was important to us as a team to be representing Canada wherever we went, and what better way than to incorporate hockey sticks into the aesthetic!?! It’s also pretty easy to find old hockey sticks up here that can be donated to the team (I remember one year getting a large donation of carbon fiber sticks that were deemed unusable/broken by a local hockey league).
For OP, the thread linked above by @leo-les is a great and modern guide to most of your questions, I’d highly recommend reading through that.
Not a guideline but something to remember - make sure that if you have any students waving it in the stands (or wherever) you let them know not to accidentally hit anyone in the face. Waving a flag carefully is more important than one might initially think. We’ve had a few near misses!