This is one school project where it pays to be full of hot air.Students from eight county schools are building their own hot air balloons in preparation for a contest this Saturday at Nunley Stadium.In addition to the student-built hot air balloons, a real hot air balloon will be on hand from 9 to 11 a.m. Everyone is welcome to come view the hot air balloon. Admission is $1.“We will have a company from Murfreesboro that will be bringing a real hot air balloon for the kids and their parents to see how it works,” said Jessica Castaneda, who is helping to organize the event. “They plan on filling up the hot air balloon and launching it a bit.