What is the gauge of the I-beams? Follow The I-beams on our buildings are not measured by a gauge. They are 3/8th inch plate stock. Related articles Where can I find more technical information on steel buildings? What if I don’t see the type of building I’m looking for? What if I need help with something after construction is complete? What comes standard on my General Steel building? What questions should I ask about warranties? Comments 0 comments Please sign in to leave a comment.