Welcome back and what a list of familiar names.
I too have been pretty much out of action for eighteen months ( wife's illness and my waterworks )
Can't believe I've just passed the three quarter century. Watch out boys and gals time really does faster the older you get
The aircraft carrier previously noted is good, Concorde is on a pontoon next to it. A few piers down is a driving range surrounded by very high nets: you know you should keep your eye in!
Hiring a bike and doing central park on a Sunday morning in good weather is magical.
I'm jealous.
Is it close to a neighbour's property? Will it need new foundations? If yes a party wall agreement will be required.
If it's to be a 'habitable' room building regs. apply.
Some good advice above. In addition I would recommend you buy the RICS form of contract for minor building works. There are others. A web search will find them.