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 is General Steel located? How much does it cost to build a mini-storage facility? What comes standard on my General Steel building? What style of roofs is available? Do you need a foundation for an RV garage? Comments 0 comments Please sign in to leave a comment.