Once all the measurements and site conditions are taken, it's time to think about profit. Some contractors base the amount of profit they build into an estimate on a few things: Risk, size of job, market, and how badly they really want that given job.
For example, a fairly low-risk job might garner a modest profit margin of 15%, whereas a high-risk job might warrant 25%. If that same job is of normal size, it warrants 15-20% profit. If it's within your normal market area, that's 10-15%. But if it's outside of your normal market, you might beef it up to 25%. If you really want the job because it could lead to more work down the road, you might peg it for just 10% profit. On the other hand, if you could care less if you win the job, stick it at the high end with 25% profit.
However you determine it, add the four categories together and divide by four to see what the profit margin should be.
Then there's one more thing to consider: the client factor. How hard will the client be to work for? Some need more attention than others, and that costs time and money. Some are harder to please, which also costs time and money. So the client factor is definitely something to think about as you're putting your final estimate together.