Any ideas to build a hippodrome for a school project

How about building it of homemade clay? Google homemade clay for lots of different recipes.

http://www.google.com/search?q=hippodrome&hl=en&source=lnms&tbm=isch&sa=X&ei=fKpEUZuJIrSxygHcoYDgBg&sqi=2&ved=0CAcQ_AUoAQ&biw=711&bih=453