Yes, you can buy a 4 plex with an FHA loan. The FHA loan limit for a four-plex is $567,500 and the maximum loan amount is 96.5% of the purchase price or appraised value, whichever is less. There is also a monthly mortgage insurance premium (MIP) that is required for all FHA loans. The MIP for a 4 plex is 0.85% of the loan amount per year, divided into 12 monthly payments.