Ground tiles disappear

Hey so I’m building a temple with modular assets I got from the market place but whenever I come to look at them form the bottom they vanish unless I’m looking at it from the top. Is their a way to see their bottoms or do I need to add additional ground panels flipped over as ceilings?

A picture would help, but it sounds like the models were created with only geometry for the tops to be optimal. No point in rendering the bottoms if they’re on the floor! Does the kit perhaps have ceiling pieces?