Frame the walls in wood like the others have mentioned. You have plenty of height there, don't use low headroom brackets on the door, those are a last resort. Rough frame your overhead door opening to the same size of the door you plan to use. Choose your door height so it leaves you at least 14" from the top of the opening to the bottom of the ceiling joists. That will leave you room for a torsion spring setup above the door with 12" radius upper track. The door will roll smoothly and still leave you room for an opener. Minimum space above the door for the opener is 2", which the 14" will provide.
Need a lot more information. Everyone is saying build a wall but no one has asked what the wall is being built on. What the carport has for a base or footers. What size the beams are and what are the beams made of. Do not forget there are plenty of portable carports that have garage doors on them. Just google it. A garage doors weight is supported on the overhead track, now if you want to put an opener on it that changes things.
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