I'm about to go to my cage builder, what should I tell them?

You'll want to print out the roll cage rules and give them a copy. Sit down with the builder and work out a cage diagram that meets the requirements and fits well in your car. Beyond the tubes, talk about what additional points will be welded to the shell. For example, it's common to have the bar above the windshield attached in several places, and having plates between the cage and both the A and B pillars is very common, even though it's not required.

Once you have a preliminary design, sketch it up on paper, take a picture, and send that off to a NRS scrutineer for a thumbs up. If you can get a thumbs-up on your design from a scrutineer before you release the builder, you will be more likely to have a build that does not require any rework. Remember that the builder doesn't issue log books, he just builds what you tell him to. So make sure the scrutineer is happy with the direction you're going before you set the builder on his way.

Agree on a price and scope of work with the builder. Get the scope documented on paper. It can be as straightforward as a list of diagram numbers from the roll cage rules, a list of tubing sizes, the number of footing plates and additional attachments, and a note about seat mounts. Additional things may come up, but get a price quoted for each additional job.

You will want to make sure you have (at least) your driver’s seat installed and in the position you want so the builder has a reference point to work from.You should also plan on taking the car to the builder with the front dash (not installed, but present) so the builder can build around or through the dash as necessary.

It is beneficial and cheap to have the suspension mount points reinforced during cage construction. Simply welding a 3/16" plate over the top of the strut towers will suffice for all first timer cars.