re: On average, what is a residential General Contactors fee/percent?

10% for overhead and 10% for profit is the industry standard. Every insurance claim and construction cost index includes this industry standard figure.

The total figure covers all his expenses to run the business and make a decent return for his work. I would avoid a builder that doesn't charge a single transparent fee for all overhead and profit. It shouldn't really matter how the builder allocates his expenses on his side, but the total should be clear to you on the proposal. Go with a fixed price contract instead of unlimited cost plus fee, and most banks will not lend without a fixed price contract.

Insurance is included as overhead and I assure you every good builder has a rate schedule for each coverage he allocates to a job. He has to track every job during the year and pay accordingly based on activity, but that shouldn't concern the buyer. All his insurance costs are charged at a fixed rate per coverage for each job, based on payroll/payments to subs (WC/GL) and the completed project value (Builder's risk/property).