If they call you it means they are checking city or county records for approved building projects and are fishing to get the job. obviously based on what you said if someone posted building plans for bids they would know why the company was calling and would not be posting here. AVOID companies like this as they are rarely local and will resell your job to another contractor at a profit without lifting a hand, which in the final analysis means you paid too much. AVOID.
Constructworks or Bid Clerk is a real business that reports upcoming construction projects to their clients. You may or may not be interested in receiving this type of information from them but they are a reputable company.
Someone called from this number and said they were requiring information on our copier in Purchasing. I immediately was on alert as we have a contract. I asked who they were working for as I knew the firm we contract with and they immediately hung up. Accent was very strong - They never identified who they were with.