I'm just getting some advice that I will be covered under the PWA.
What do you mean by that?
What "cover" do you think the PWA provides?
His responsibility regarding the quality of design and construction, and your remedies and rights should something go awry have nothing to do with the PWA - they are the same whether he serves a notice on you or not.
The Act is there to give you the right to be
informed that certain works which impact a "party wall" are planned. It does not give you any right to deny permission for the work, and it does not contain any provisions which would allow you to bring a halt to the work if you haven't been notified apart from going to cou£t and taking out an injunction. It does give you the right to have a surveyor appointed at his expense if you are concerned that the work won't be properly done.
That really is the main question - how happy are you that he will have the work done properly? It's his building, so he isn't going to want to see the top half fall into the garden - as long as he's had proper structural design done, which has been approved by Building Control, and the work is inspected, your flat will be fine, and if it isn't the PWA won't help you.
Yes, he
should serve a notice as the Act requires him to do, but if he doesn't there's nothing you can do apart from getting so£icitors involved and making an enemy of him.
But do take photographs, with that day's newspaper in the shots, showing lack of cracks, level floors, doors and windows fitting, the height of any wall mounted furniture above the floor etc, so that if anything goes awry you have made it easier to prove that the wall cracked and your floor dropped shortly after the lower half was removed.