I regularly prune any tree branches (including neighbours) that are within 1.5-2 metres of the roof (double story house though), and a bit more if they are taller than the house. Seems to work well enough that they dont annoy us anymore. There are probably enough other roofs that are easier to get to than ours now...
The next was going to be installing one of those possum boxes not too far from the house, the theory is that being territorial if one takes over the possum box then others will keep their distance.
There is no point get a possum "professionally" removed from the roof and take no other measures, as they have to release back into the same area!
As an aside,
I had a problem with bats and a possums fighting over palm tree fruits, and keeping us awake all night! I now also prune the palm trees flower stalks...no more fruit, no more noise ;D.