If your apartment is already wired for cable does a cable company need to install their own and should they need to do any outside installation?

It really depends on your cable company. In most cases, they'll do the outside installation and just connect to your system, but that's where their responsibility will end. From that point on, and poor TV signal issues will then be the responsibility of the apartment owner and it will fall upon them to correct any signal issues you may have due to poor signal strength or faulty wiring.