I am not clear on what the actual problem with the roof of your slide out is. If the roof has to be replaced due to severe damage then that is not a do-it-your-selfer job and you should take it in and have a professional repair it for you.
If you have some minor cracks or leaks in the roof you can use a product called Eternabond Roof Seal to easily patch the minor cracks and stop the leaks. Take a look at the video below to see how easy it is to use. Even though this is not a slide out roof you would use the same techniques to repair your slide out roof.
Everything-About-RVing.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com.