I am in business for myself and was faced with the same decision to leave the safe secure paycheck behind to pursue my own dreams. My best advice is to start small to grow big. I have done many ventures, some great, some bad. Why would you quit your job to do books and advertising which could be done on the weekends or after u got hom from work. Keep your positive cashflow from work as you start the roofing on the side. If you get so busy that your 9-5 gets in the way, then its pretty easy for you to decide to move in the direction of dedicating all of your time to your business. For now the best bet is to pull 65hr work weeks, 40 to the 9-5 and 25 to your biz.
The biggest mistake you can make is not having enough money to get through the inital startup which is usually slower and less stellar than you expect. Anticipate the worst and hope for the best. DO NOT quit your job until you KNOW your job is keeping you from making more money.