My dryer vent goes from the second story to the roof. The problem is that I can't reach the roof. I bought one of those dryer vent cleaners that you can put on your drill and spin it up the vent. Currently it goes 8 feet. Could I buy another one and go up 16 feet and just push or pull the excess lint all the way from the roof top or is it better to have someone do it from the roof. Also, are there other things a professional will do besides use a long brush?
My experience using those brushes is that it's difficult to tell if you're pushing on a lint blockage, a turn in the pipe, or your knocking the cap off the end of the pipe. So if at all possible, you should have the end open and/or connected to a vacuum. You don't want this tool ramming into the motor in your dryer, nor do you want it knocking the damper off the outside of your house. In your case, that's going to require someone on the roof.
You can get close, keeping track of how many segments of the cleaning tool you used to get to the roof in a previous cleaning, and then stop a few feet early. But as Michael says, the cap itself should be cleaned since lots of lint will build up there.
You can use the brush up the vent from the inside and this will clean a part of the pipe that the brush can access. The problem that you may still have is that the vent pipe normally has a weather and critter shroud over the top of it at the roof. Dryer lint can build up at this point and clog the very top of the pipe. Your brush is unlikely to be able to clean this part of the vent and thus access via the roof will be needed to inspect the vent and clean it if necessary.
In my experience, I tool bought one a DIY 8 foot cleaner that is actually fiberglass and comes with 4 two foot sections that attached to a 4 inch brush. The problem here is you MUST only go a few inches at a time an pull back to the point of exiting. If you drive the entire length, you are only packing all the lint to a point that may be open or screen creating a larger issue and potentially larger bill if you need hire a person to locate the exit vent. These condos/townhome structures are a P.I.T.A. and once the duct work is clean, I would advocate cleaning with your home snake/tool periodically to decrease blockage at the exit point. God forbid the home builders place the exit point 8 feet off the ground versus the ceiling.