Does the current zoning allow it? If not, can you rezone?
Be aware of new rules for new construction ie replacing old windows, furnaces, roofs or wires to old part of building plus home warranty implications.
Might not be as simple as stated.
Check with city planning department.
Financing options, assuming permitting not a problem, are basically based on current property value plus construction cost and assuming sufficient networth bank will lend up to 75% of it. Private lenders similar but more expensive at low double digit rates counting upfront fees and monthly fees until done, then refi fully leased with big bank based on income. (Assuming a rental not a condo project)
Thomas Beyer, Asset Manager, Investor, Asset Improver, Author, Father, Mentor
www.prestprop.com