In addition to the method of securing the laying of sidewalks set out in Section forty-nine of this Charter, the Council of said City may cause any sidewalk to be constructed, laid, re-laid, or otherwise permanently improved in the City of Dunbar in the following manner and upon the following terms: Notice shall first be given the abutting property owners by publication in some newspaper of general circulation in the City, giving location, estimated frontage and depth, but no error in said publication shall in any way affect the validity of the certificates hereinafter provided for, or any of them. The contract for same shall, after due advertisement in which Council shall reserve the right to reject any and all bids, be let to the lowest responsible bidder and upon completion and acceptance of the work, Council shall order the Mayor and City Clerk to issue to the contractor doing the work a certificate for the amount of the assessment to be paid by the owner of any lot or fractional part thereof fronting on such sidewalk, and the amount specified in said assessment certificate shall be a lien in the hands of the holder thereof upon the lot or part of a lot fronting on such sidewalk and such certificate shall draw interest from the date of said assessment, and the payment may be enforced in the name of the holder of such certificate by a proper suit in equity in any court having proper jurisdiction to enforce such liens, and Council shall fix the amount of such assessments and do all things in connection therewith necessary to make them valid and do all other things in connection therewith as is provided for paving or improving streets and alleys and such certificates shall be issued for each abutting lot or portion thereof payable six months from the date of the completion and acceptance of the work and shall be a lien in the hands of the holder thereof upon the particular lot against which they are assessed in the same way and manner as assessments for street paving liens under the other provisions of this Charter; provided, however, that Council shall not order any but concrete sidewalks; and provided, further, that Council shall not advertise for bids for anyone letting of less than five thousand (5,000) square feet; and further provided, that Council shall not receive any bids or let any sidewalk contract between the first day of October and the first day of March of any years. Nothing in this section shall be so construed as to prevent any abutting lot owner from having his own sidewalk put in if done before the advertising hereinbefore mentioned, and provided same is done according to the lines, grades and specifications of the City Engineer, for which no charge shall be made. The total cost of construction, laying, re-laying or otherwise permanently improving any sidewalk or walks shall be borne by the owners of the land abutting upon said sidewalk or sidewalks according to the following plan, that is to say, payment is to be made according to the proportion which the number of square feet in front of any lot or portion thereof bears to the whole letting. The contract for sidewalks referred to in this section need not be for one continuous sidewalk, but the five thousand square feet required for a letting, as aforesaid, may be made up of or composed of any number of sidewalks in any part of the City.