How should I improve an SFH that I want to hold for 5 years?

[Sean Yan]

Background

     - Location: Bay Area Peninsula

     - House Price: ~$1M, Mortgage $700k

     - Rent with similar square footage:  $4000/month

Running the number, it looks like it marginally break-even.

But I really wanted to have some cashflow during my holding years, so I am thinking to make an ADU. Here is my dilemma

- adding ADU itself cost money anyway (though a bit less than normal expanding?), but ADU won't add selling value as normal expanding

    - doing normal expanding cost equal (if not more) money, but will add less cash-flow during my holding years      

I wonder if there is a way for me to do ADU now, and later on convert ADU to normal square footage when I plan to sell.

Is this a good idea? (I am a new investor)