For a co-op apartment of 800 sq. ft, is it possible that we can DIY and hire architect/licensed technicians to sign off the paperworks? I'm new to this but my understanding is that $125 per sq. ft. is the bare min to renovate an apartment in NYC (i.e. wood flooring, painting, renovate the kitchens & bathrooms without touching the plumb or wires), which means it might cost up to $100k to renovate my old apartment.

My dad was a retired contractor in HK working for those stuff but he's not sure what the law is in the US to renovate a co-op apartment. My understanding is that we need the board's approval before we can start renovation but I'm not sure how difficult it is to get it done all my yourself.

What part/step of the renovation must be done by the professionals? And if we were to hire say a professional just to sign off the paper works, how much is it usually gonna cost?

Thanks!