You can, but it's always best to take care of the whole problem rather than slap a bandaid on. The roof will need to be repaired to prevent future damage, but the current damage will need to be addressed. Water damage, if left on its own, will cause mold growth and your structures may begin to rot. Drying out the space as fast as possible will prevent that, and homeowners rarely have access to the type of equipment that can accomplish it.