if you have to pay ... well whats the difference between the RBC and any other worldly building company?
The "worldly" building company is (at least, should be) a licensed, insured contractor. They will pull the required permits, pass the inspections, and there is somebody to stand behind the work.
If a volunteer gets hurt on the job, who is responsible? If there is no insured contractor involved, I doubt there would be workman's compensation coverage.