Hi Tom -- as a lifelong Marvel Fan, and an avid craft and costume builder, I'm wondering if there is a layman's version of Marvel views things like fans making items like Stark Industry t-shirts or aluminum shields -- items which pay homage to the comics but are not being sourced to China by the thousands.
So long as you’re not building such things for profit–selling them–but are only making them for your own cosplay use, I don’t think there’d be a problem.