You can sue a contractor for unreasonable delay. We would need to know more information to determine if a six month delay was unreasonable in your situation. Generally, a court will evaluate the following criteria:
The delay was caused by the contractor's fault and that it was not foreseeable;
whether the delays were in bad faith; and
whether the contract “contemplated and excused” the delays.
You can read my article on unreasonable delay for more detail as well as the delay section of our bad contractor article.
As for immediate actions you can take:
Review your contract to determine how delays are handled and what the penalties are. (For example, is there a liquidated damages clause.) In addition to provisions regarding delays, also review the "force majeure" provision of the contract.
Keep good records of all communications with your contractor, including emails, text messages, and phone calls.
Document the delays, including the date the delay began, the reason for the delay, and the impact of the delay on the project.
If you would like to speak to a real estate attorney to discuss your case, please contact us at (303) 688-0944 for a free case assessment. We likely can help bring the delay to conclusion.