DIY Building a deck/stairs on multifamily

[Willy Vasquez morales]

I want to replace the deck/stairs on the back of my two family. The deck/stairs on the back go to the second unit on the second floor. It is in bad shape. it is not falling apart though. 

I am a handy man and i do all the maintenance. I find that i do a better job than the guys i hire. Even the really good ones, the job i hire them to do is because i didnt have the time. 

I live in NH and i was wondering what sort of regulations are there? Would i need to hire an insured company to do the work? 

Any thought or idea would be really appreciated.

thanks,