What could be making so many kids sick?

I am in my high school's marching band. The section of our school where our band room is just got the roof replaced and during the process a huge hole was made leaving behind tons a debris on our floor. Everything was cleaned before anyone was allowed back in. About one week later a large amount of band kids started to feel sick. We all feel nauseous, congested in the chest and head, have a sharp pain in te middle of our ribs, and feel dizzy and head-achey. We heard that there is 25% of an unidentified substance in the air in this section of the school, but this could be false. What could make so many kids feel this sick? Does it have anything to do with the roof caving in? If you have any ideas please voice them, we would greatly appreciate it! Thanks for helping us feel healthier! =]