Every month any credit will have to be treated as common credit. Then on the basis of carpet area identify the portion of credit pertaining to residential and commercial.
That pertaining to residential completely reverse. That pertaining to commercial avail (assuming you are selling these units before completion). In case in commercial portion you are able to ascertain how many units you would be selling post completion, to that extent credit can be reversed every month.
Finally, on completion, the credit relating to the commercial portion can be re-worked based on the actual area sold after completion.