You need to carefully read your written deed to the townhouse that you are writing about to answer your question. In some circumstances ownership of townhouses can be owned as tenancies in common with other people (TIC). You need to read your deed to see if you own the property all yourself or not (as a tenant in common).Your neighbor may be confused about the roof being common property as opposed to being a common maintenance issue for the association to fix. I suggest reading the presumed recorded covenants, conditions & restrictions on your home to answer this question about common area maintenance.