Compressed Air Piping

Copper is easy to install and will last forever but is very expensive these days.
Definitely do not use raw iron pipe, it will rust and contaminate your air. Galvanized is an option.
I did my garage with the same stuff Jim posted above. Its affordable and is fairly easy to install. Install an air fitting about every 6-8 feet in your garage. The more the better. Also good to install a water drop on each leg like you see pictured. I have a couple regulators in my system so I can run different pressures without adjusting all the time.