All porches, porticoes or other elevated structures one or more stories high over any pavement or sidewalk of the City in front of any building or lot and which are supported by posts or pillars stationed inside of eight feet clear from the front of the houses or lots on any street or which may have a roof or cover less than eight feet clear from the sidewalk or pavement and all doorsteps, stoops or porticoes in front of any dwelling or other houses in the City fronting on any street thereof, which extend more than four feet over the pavements or sidewalks of any street or which do not leave at least five feet of such sidewalks for free and unobstructed passage in front thereof, be and the same are hereby declared to be public nuisances; and the Planning and Public Works Director, when so directed by the legislative body in any case, shall give notice to the owners of any such porches, porticoes or elevated structures aforesaid or of such doorsteps, stoops or porticoes declared in this section to be nuisances or to the tenant of the premises to which they are attached and belong for the removal of such posts, pillars, porches, porticoes, doorsteps or other obstructions above mentioned or the modification thereof in such manner as the legislative body may direct so as to abate or remove the nuisance within 20 days from the delivery of such notice; and if the same are not removed or modified in accordance with such notice at the end of such 20 days, the owner of such building or premises to which the nuisance is attached or who owns such nuisance shall be subject to prosecution for violation of this section, and such nuisance shall be subject to abatement by the Planning and Public Works Director at the cost of the owner thereof and in case of his refusal to pay such costs shall constitute a lien upon the property in favor of the City to be collected in the same manner as city taxes are collected.