(4) The total cost referred to in sub section (2) and sub section (3) shall consist of the market value of the site in which the building is constructed, the cost of construction of the building and the cost of provision of any one or more of the amenities specified in Schedule I as on the date of application for fixation of fair rent; Provided further that the cost of provision of amenities specified in Schedule I shall not exceed 397 (i) in the case of any residential building, fifteen per cent; and (ii) in the case of non residential building, twentyfive per cent, of the cost of site in which the building is con structed and the cost of construction of the building as determined under this Section." "5.(a) The cost of construction of the building including cost of internal water supply, sanitary and electrical installations shall be determined with due regard to the rates adopted for the purpose of estimation by the Public Works Department of the Government for the area concerned.