Said commission shall at the beginning of each calendar month render a detailed statement to the county auditor of Hennepin County and to the city controller of the city of Minneapolis, respectively, of all its expenses necessarily incurred for the purposes contemplated by sections 383B.75 to 383B.754 during the last preceding month in or with reference to portions of said building used or occupied by the county and by the city, respectively, including the proper portions of all expenses rendered for the common benefit of the county and city and properly chargeable to each of such municipalities; whereupon it shall become the duty of the proper officers of said county and of said city to forthwith draw warrants upon their respective treasurers, each for the amount of the account rendered against it by said commission, and it shall be the duty of the treasurer of said municipal building commission to forthwith pay to the parties properly entitled thereto the several amounts specified in said accounts rendered.