Thanks for sharing your question about painting your metal carport. I recommend giving the entire metal frame a wash with Monarch 3L Sugar Soap with Mould Remover in combination with Scotch-Brite 155 x 100mm Heavy Duty Scourer Pad - 6 Pack. Make sure to wash everything off before you start painting.
If you prefer a spray-painted finish I recommend using Ozito 400W Power Paint Spray Gun. However, you can also use a brush or roller to apply the paint. Please be aware that these will either leave paint brush marks or roller marks on the surface.
I suggest lightly sanding the surface of the metal frame to prepare it for painting. Once you've sanded it wipe down the surface with a damp cloth to remove dust and debris on the surface. I suggest using the White Knight Rust Guard Medium Grey Metal Primer Paint to prime the surface of your metal frame. Once the primer is totally dry, I recommend White Knight Rust Guard Satin White Quick Dry Advanced Enamel Paint as your top coat. Please note that this topcoat can be tinted to your preferred colour.
Here is a handy guide: Paint sprayer buying guide: how to choose a paint sprayer
Here is a link to a project that uses a spray gun: How to paint a fence with a spray gun.
If you have any other questions we can help with, please let us know.
Keep us updated on your progress @kagomechan, and please reach out if you need further assistance. I trust our members will be keen to see your results.