Neighbours rights to house access during reno

Neighbour is doing a reno to extend up, with one side of our freestanding house being the border/"or functional fence" between the homes and the distance between the two only a few fists.

What are they allowed to do / not do with our house side being the border, e.g. can they go on our roof for periods of time or put anything into our side of house as part of the construction process, e.g. scaffolding?

not without your permission AFAIK.

They cannot access your property or put anything on your property without your permission.
If they do request any access first ask to see evidence that they have insurance for any potential damage of neighbouring, i.e. your, properties and discuss the issue with your insurance company

If works protection is required your neighbours may be granted access under legislation, however they cannot access your property for construction works.

The only thing to add to these comments is that where possible it's always good to try and work with people than just say "no" because you can.
Having someone build/renovate next to you can be a real annoyance, but in the big scheme of things it is only temporary. Often if you can be accommodating to your neighbours/builders requests it can actually simplify and hasten the building process lessening the ultimate impact on you. Sure it's not always the case and some may take advantage of any concessions you give them, but in my experience if everyone tries to work together and find mutual understanding then the process moves on with minimal inconvenience.
Ultimately you will live next to your neighbours much longer than the whole building process so maintaining good relations where possible is always a good practice, plus you never know when you might need some concession from your neighbour.
Hope it goes well for you.