SVG University just added several videos for dealing with objections. I don't agree it is the key but it is important. I happen to think it is more important to understand how to ask probing questions. The vast majority of roof buyers have a passive need. That's particularly true for insurance work in an area where there aren't frequent storms. By asking appropriate questions, you can begin to turn that passive need into an active need. Active needs are people that have a leak, people that see shingles blowing off, people that know they just got hit with huge hail, etc.. Unfortunately, in most cases, 95% to 98% of the people you approach are in the passive category. The good news with people with an active need is they're ready to buy from someone. That bad news is, they're probably getting multiple bids.
I would highly recommend you read Question Based Selling by Thomas A Freese, and SPIN Selling by Neil Rackham (Situation, Problem, Implication, Need). For more hustle, hard core d2d selling, read Grant Cardone Sell or be Sold. For old school, Zig Ziglar Selling 101.