Of course that increases with thickness, the addition of insulation boards, radiant heating, rockwool, etc.

Additionally, the application and approval process for USDA multifamily loans can be complex, so it's advisable to work with a qualified lender experienced in USDA loans and the multifamily housing sector.To determine if a specific multifamily property is eligible for a USDA loan, it's recommended to consult with a USDA-approved lender or reach out to the USDA Rural Development Office in your area.

Overall, we were able to create a new product, offering a first-floor Main Bedroom Suite and three additional bedrooms on the second floor.

Do a full on purchase at a discounted value based on your retained equity. 

Most people do not have the cash to obtain the cash discounts.  

Additionally, thoroughly research the local real estate market, economic conditions, and renter demand to make an informed decision about whether the condo purchase aligns with your investment objectives.

For us, our current investment strategy we take advantage of, is primary home loans by moving out and renting the previous one and purchasing one additional property every year. you're able to buy a single family home or a multifamily up to 4 units every single year.

In addition to ensuring that the room is built to the proper load bearing capacity as @Mike Reynolds mentioned, you should also keep in mind that you need a second egress point, such as an egress window, for any habitable room especially if it is designed for sleeping purposes.

Additionally, the strong job market and growing population point to continued demand for multi-family units.

If you already have a property under contract or have a property in mind that you see as 60k all in you should build in 10-15% in additional costs as a contingency fund because things happen.