FHA 4-unit multi-family to 5-unit?

[Michael Crouse]

I'm currently looking at a 4-unit multi-family for my first home purchase. The property is currently fully rented with good tenants, however it has a very open and empty basement with the back exposed. I'm considering the possibility of buying the property with an FHA loan, and then finishing the basement into an owners unit. The property is currently zoned commercial. Are there any major problems I'll likely run into with this?