I always use the Buildings plugin in Josm for mapping buildings. I create circular or rectangular buildings or buildings with right angles. I also leave a gap between two buildings to avoid overlap. In case some buildings get overlapped, I remove them with help of warnings shown while uploading data in JOSM. I have been using the rules of mapping buildings every time I map tasks. Being a person who also uses data from OSM I tend to map more carefully, I am confused about the errors that occurred. In any case, if I had made mistakes I will be more careful from here on. Thank you for the comment. @Frans S