You need to think carefully about what you are doing if you want to attempt to work effectively as a roofer. Your customers will be counting on you, and you need to make sure you don't let them down by making simple but costly mistakes. Sadly, it is easy to make these types of mistakes, and you might end up paying for it in terms of lost business if you are not careful.
Always quote a fair price to your customers. You might be tempted to quote higher than necessary to account for variables that might come into play while doing your work. However, you should avoid doing so because that is one of the quickest ways to lose your customers. They already don't want to be involved in having to repair the roof in the first place. If you add on to that by quoting them a price that is clearly beyond what it will truly cost to repair, then you are adding insult to injury. You don't have to put your customers in that position, and you shouldn't.
Finally, make sure you use quality materials for all of your jobs as well. Customers will appreciate receiving something that is built to last.