How do I find financial information about a construction employer that I am interviewing with?

It really depends on whether they are public ally or privately held. If a construction employer is public ally traded, they must report their earnings to the SEC (US Securities and Exchange Commission). For example, if they are traded on the Nasdaq stock market, you can look up their exchange symbol on the Nasdaq website and review their financial history. You can also request their Annual Report.
If the construction employer is privately held, it is much more difficult to obtain their financial status. One idea, however, is to review trade magazines which often have industry rankings or may have written articles on the construction employer.
Look at the competition as well to try and see where they fit. Also, see if you can find out if there have been wide fluctuations in the number of employees over the past few years. Check to see if there have been downsizings or if it has shown steady growth over the years