Ammonia is a cleaning product (smells like hell) and you should in theory beable to get it at most places that sell cleaning stuff, a hardware store should have it.Def worth a try - the damage critters can cause in your roof is not limited to pulling off tiles and eating insulation - they can also get going on electrical wires and cause fires. Not to alarm you or anything, but it is very hazardous for them to be up there.