If you are building a new home or making substantial changes to an existing home ( change the roof line eg: add a room ) then you need to obtain a construction loan. Not all lenders offer construction and of those that do, most offer at a higher interest rate and with additional fees. These may be additional establishment fees and inspection or progress payment fees. Usually you are restricted to a variable interest rate although most construction home loans are IO until the construction is complete then revert to P&I.
If you are embarking on a renovation it is vitally important that you get adequate finance in place before you pick up the hammer. Lenders are not interested in half completed jobs or borrowers who have maxed out their credit cards and missed a few payments.